Ch1-Organic Unit 4

11Organic ChemistryOrganic Chemistry

uni t

In this unit, you will be able to

demonstrate an understanding of the structure of various organic compounds, and ofchemical reactions involving these compounds;

investigate various organic compounds through research and experimentation, predictthe products of organic reactions, and name and represent the structures of organiccompounds using the IUPAC system and molecular models; and

evaluate the impact of organic compounds on our standard of living and theenvironment.

Overall Expectations

Eugenia KumachevaAssociate ProfessorUniversity of Toronto

By clever synthesis, organic chemists obtain new moleculeswith fascinating architectures, compositions, and functions.My research group studies polymers (long-chain moleculeswith many repeating units) that possess fluorescent, non-linear optical, and electroactive properties. In particular, weare interested in nanostructured materials made from verysmall polymer particles. For example, we work on synthe-sizing polymers for high-density optical data storage. One of

the materials designed and created in our laboratory is often pictured as a pieceof new plastic about the size of a cube of sugar on which one can store theentire Canadian National Library collection. Other polymers can change theirtransparency when illuminated with high-intensity light. The coatings andfilms made from such polymers can be used to protect pilots eyes from dam-aging laser light and in optical networks in telecommunication. New syntheticpolymers have found a variety of exciting applications, and their use in mate-rials science will grow even more rapidly in the future.

Unit 1OrganicChemistry

ARE YOU READY?

Understanding Concepts1. Write the IUPAC name for each of the following compounds.

2. Draw structures of the following compounds.(a) pentane(b) 2,2-dimethylheptane(c) 4-ethyl-1-methylcyclohexane(d) 5-methyl-1-hexene(e) 1-butyne

3. Write a balanced chemical equation to show the complete combustion ofheptane, a component of gasoline.

4. Which of the following are structural isomers?

Concepts

IUPAC nomenclature ofsimple aliphatichydrocarbons, includingcyclic compounds

structural and geometricisomers

characteristic physicalproperties and chemicalreactions of saturated andunsaturated hydrocarbons

electronegativity and polarbonds

chemical bonding, includingionic bonds, covalent bonds,hydrogen bonds, van derWaals forces

formation of solutionsinvolving polar and nonpolarsubstances

Prerequisites

H

H

H

H

H H

CCC

CCC

HH

HH

HH

H

HH

H

H

H

H H

CCC

CCC

HH

H

H

C C C C C C H

H

H H

HH

H

H

CCH3

CH3 CH3

CH3C

(a)

C

CH2 CH3

CH3

CH3

CH2

CH3

CH2 CH2 CH3

CH3

(a) (b)

(b)

(c)

(d)

4 Unit 1 NEL

Unit 1

5. Predict the relative boiling points of the following two compounds.(a)

(b)

6. Predict the relative solubilities of the following compounds in water.

7. Write the following elements in order of increasing electronegativity: carbon,chlorine, hydrogen, nitrogen, oxygen, sulfur.

8. For each of the following compounds, describe the intramolecular bond typesand the intermolecular forces.(a) CH4(b) H2O(c) NH3

Applying Inquiry Skills9. Three liquids are tested with aqueous bromine (Figure 1). Samples of the solu-

tions are also vaporized and their boiling points determined. The evidence isshown in Table 1.

Which of the liquids is pentane, 2-methylbutane, and 2-methyl-2-butene?

Safety and Technical Skills10. List the safety precautions needed in the handling, storage, and disposal of

(a) concentrated sulfuric acid;(b) flammable liquids, e.g., ethanol.

NEL Organic Chemistry 5

CH3

CH3CH2CH2CH2CH3

CH3

CH3CCH3

pentane

2,2-dimethylpropane

Table 1

Compound Liquid 1 Liquid 2 Liquid 3 Br2(aq) test no change turns no change

colourless

boiling point (C) 36 39 12

H

O

C C H

H

O H

H

H

H

H H

H

CCC

CCC

H

C

H

HH(a) (b)

Figure 1

liquid 1 liquid 2

11 Organic Compoundschapter

Organic Compounds

In this chapter,you will be able to

classify organic compoundsby identifying their functionalgroups, by name, bystructural formula, and bybuilding molecular models;

use the IUPAC system toname and write structuraldiagrams for differentclasses of organiccompounds, and identifysome nonsystematic namesfor common organiccompounds;

relate some physicalproperties of the classes oforganic compounds to theirfunctional groups;

describe and predictcharacteristic chemicalreactions of different classesof organic compounds, andclassify the chemicalreactions by type;

design the synthesis oforganic compounds fromsimpler compounds, bypredicting the products oforganic reactions;

carry out laboratoryprocedures to synthesizeorganic compounds;

evaluate the use of the termorganic in everydaylanguage and in scientificterminology;

describe the variety andimportance of organiccompounds in our lives, andevaluate the impact oforganic materials on ourstandard of living and theenvironment.

In a supermarket or in a pharmacy, the term organic is used to describe products thatare grown entirely through natural biological processes, without the use of syntheticmaterials.Organic fruits and vegetables are not treated with synthetic fertilizers or pes-ticides; organic chickens or cows are raised from organically grown feed, without the useof antibiotics. The growing organic market, despite higher prices over conventionallygrown foods, indicates that some consumers believe that molecules made by a livingplant or animal are different from, and indeed better than, those made in a laboratory.

In the early 18th century, the term organic had similar origins in chemistry. At thattime, most chemists believed that compounds produced by living systems could not bemade by any laboratory procedure. Scientists coined the chemical term organic to dis-tinguish between compounds obtained from living organisms and those obtained frommineral sources.

In 1828, a German chemist, Friedrich Whler, obtained urea from the reaction of twoinorganic compounds, potassium cyanate and ammonium chloride. Since then, manyother organic compounds have been prepared from inorganic materials.

Organic chemistry today is the study of compounds in which carbon is the principalelement. Animals, plants, and fossil fuels contain a remarkable variety of carbon com-pounds. What is it about the carbon atom that allows it to form such a variety of com-pounds, a variety that allows the diversity we see in living organisms? The answer lies inthe fact that carbon atoms can form four bonds. Carbon atoms have another specialproperty: They can bond together to form chains, rings, spheres, sheets, and tubes ofalmost any size and can form combinations of single, double, and triple covalent bonds.This versatility allows the formation of a huge variety of very large organic molecules.

In this chapter, we will examine the characteristic physical properties of families of organicmolecules, and relate these properties to the elements within the molecule and the bondsthat hold them together. We will also look at the chemical reactions that transform oneorganic molecule into another. Finally, we will see how these single transformations can becarried out in sequence to synthesize a desired product, starting with simple compounds.

6 Chapter 1 NEL

1. Much of the research in organic chemistry is focused on a search for new orimproved products. Suppose that you wish to develop a new stain remover, or a moreeffective drug, or a better-tasting soft drink. What should be the properties of theingredients of your chosen product?

2. In the field of biology, complex systems have been developed to classify and namethe countless different living organisms. Suggest an effective method of classifyingand naming the vast range of organic compounds that exist.

3. From your knowledge of intramolecular and intermolecular attractions, describe fea-tures in the molecular structure of a compound that would account for its solubilityand its melting and boiling points.

4. What does organic mean? Give as many definitions as you can.

REFLECT on your learning

Organic Compounds 7NEL

TRYTHIS activity How Do Fire-EatersDo That?Have you ever wondered how some street performers can extinguish aflaming torch by swallowing the fire, without burning themselves? Here isan activity that might help you answer the puzzle of how do they do that?

Materials: 2 large glass beakers or jars; 2-propanol (rubbing alcohol); water;table salt; tongs; paper; safety lighter or match

2-propanol is highly flammable. Ensure that containers of the alcohol are sealed and stored far from any open flame.

In a large glass beaker or jar, mix together equal volumes of 2-propanoland water, to a total of about 100 mL.

Dissolve a small amount of NaCl (about 0.5 g) in the solution, to addcolour to the flame that will be observed.

Using tongs, dip a piece of paper about 5 cm 5 cm into the solutionuntil it is well soaked. Take the paper out and hold it over the jar for a fewseconds until it stops dripping.

Dispose of the alcohol solution by flushing it down the sink (or asdirected by your teacher), and fill another beaker or jar with water as aprecautionary measure to extinguish any flames if necessary.

Still holding the soaked paper with tongs, ignite it using the lighter ormatch.(a) From your observations, suggest a reason why fire-eaters do not

suffer severe burns from their performance.

8 Chapter 1 NEL

1.11.1 Functional GroupsWith the huge number of organic substances, we would havegreat difficulty memorizing the properties of each compound.Fortunately, the compounds fall into organic familiesaccording to particular combinations of atoms in each mol-ecule. The physical properties and reactivity of the compoundsare related to these recognizable combinations, called func-tional groups. These functional groups determine whetherthe molecules are readily soluble in polar or non-polar sol-vents, whether they have high or low melting and boilingpoints, and whether they readily react with other molecules.

So, if we can recognize and understand the influence ofeach functional group, we will be able to predict the proper-ties of any organic compound. If we can predict their prop-

erties, we can then design molecules to serve particular purposes, and devise methodsto make these desired molecules.

In this chapter, we will discuss each organic family by relating its properties to thefunctional groups it contains. Moreover, we will focus on how one organic family can besynthesized from another; that is, we will learn about the reaction pathways that allowone functional group to be transformed into another. By the end of the chapter, we willhave developed a summary flow chart of organic reactions, and we will be able to plansynthetic pathways to and from many different organic molecules. After all, designing thesynthesis of new molecules, ranging from high-tech fabrics to designer drugs, is one ofthe most important aspects of modern organic chemistry (Figure 1).

Before discussing each organic family, lets take a look at what makes up the func-tional groups. Although there are many different functional groups, they essentially con-sist of only three main components, one or more of which may be present in eachfunctional group. Understanding the properties of these three components will make iteasy to understand and predict the general properties of the organic families to whichthey belong (Figure 2):

carboncarbon multiple bonds, CC or CC single bonds between a carbon atom and a more electronegative atom,

e.g., CO, CN, or CCl

carbon atom double-bonded to an oxygen atom, CO

Figure 1The design and synthesis of newmaterials with specific properties,like the plastic in this artificial skirun, is a key focus of the chemicalindustry.

H

H C C H

H

ethene (an alkene)

H C O

H

methanal (an aldehyde)

H C O H

H

H

methanol (an alcohol)

Figure 2Examples of the three main compo-nents of functional groups:(a) A double bond between two

carbon atoms(b) A single bond between carbon

and a more electronegativeatom (e.g., oxygen)

(c) A double bond between carbonand oxygen

organic family a group of organiccompounds with common structuralfeatures that impart characteristicphysical properties and reactivity

functional group a structuralarrangement of atoms that impartsparticular characteristics to the molecule

(a) (b)

(c)

When atoms have different elec-tronegativities (Table 1), thebonds that form between themtend to be polar, with the electronsdisplaced toward the more elec-tronegative atom. Many propertiesof compounds of these elementsare explained by the polarity oftheir bonds.

LEARNING TIP


CarbonCarbon Multiple BondsWhen a C atom is single-bonded to another C atom, the bond is a strong covalent bondthat is difficult to break. Thus, the sites in organic molecules that contain CC bondsare not reactive. However, double or triple bonds between C atoms are more reactive.The second and third bonds formed in a multiple bond are not as strong as the first bondand are more readily broken. This allows carboncarbon multiple bonds to be sites for reac-tions in which more atoms are added to the C atoms. The distinction between single andmultiple bonds is not always clear-cut. For example, the reactivity of the six-carbon ringstructure found in benzene indicates that there may be a type of bond intermediatebetween a single and a double bond. This theory is supported by measured bond lengths.You will learn more about the strengths of single and multiple bonds in Chapter 4.

Single Bonds Between Carbon and MoreElectronegative AtomsWhenever a C atom is bonded to a more electronegative atom, the bond between theatoms is polar; that is, the electrons are held more closely to the more electronegativeatom. This results in the C atom having a partial positive charge and the O, N, orhalogen atom having a partial negative charge. Any increase in polarity of a moleculealso increases intermolecular attractions, such as van der Waals forces. As more forceis required to separate the molecules, the melting points and boiling points alsoincrease (Figure 3).

If the O or N atoms are in turn bonded to an H atom, an OH or NH group isformed, with special properties. The presence of an OH group enables an organicmolecule to form hydrogen bonds with other OH groups. The formation of thesehydrogen bonds not only further increases intermolecular attractions, it also enablesthese molecules to mix readily with polar solutes and solvents. You may recall the sayinglike dissolves like. The solubility of organic compounds is affected by nonpolar com-ponents and polar components within the molecule. Since N is only slightly less elec-tronegative than O, the effect of an NH bond is similar to that of an OH bond:NH groups also participate in hydrogen bonding.

Section 1.1

Figure 3(a) Nonpolar substances, with

weak forces of attractionamong the molecules, evaporate easily. In fact, theyare often gases at room temperature.

(b) Polar substances, with strongforces of attraction among themolecules, require considerableenergy to evaporate.

(a) (b)

Table 1 Electronegativities ofCommon Elements

Element Electro- negativity

H 2.1

C 2.5

N 3.0

O 3.5

10 Chapter 1 NEL

Double Bonded Carbon and OxygenThe third main component of functional groups consists of a C atom double-bonded toan O atom. The double covalent bond between C and O requires that four electrons beshared between the atoms, all four being more strongly attracted to the O atom. This makesthe CO bond strongly polarized, with the accompanying effects of raising boiling andmelting points, and increasing solubility in polar solvents.

Multiple bonds between C atoms

CC Unlike single CC bonds, double and triple bonds allow atomsCC to be added to the chain.

C atom bonded to a more electronegative atom (O, N, halogen)

CO Unequal sharing of electrons results in polar bonds,CN increasing intermolecular attraction, and raising boiling and CCl, CBr, CF melting points.

COH or These groups enable hydrogen bonding, increasing solubilityCNH in polar substances.

C atom double-bonded to an O atom

CO The resulting polar bond increases boiling point and melting point.

Three Main Components of Functional GroupsSUMMARY

PracticeUnderstanding Concepts

1. Explain the meaning of the term functional group.

2. Are double and triple bonds between C atoms more reactive or less reactive thansingle bonds? Explain.

3. Would a substance composed of more polar molecules have a higher or lower boilingpoint than a substance composed of less polar molecules? Explain.

4. Describe the three main components of functional groups in organic molecules.

Section 1.1 QuestionsUnderstanding Concepts

1. What is the effect of the presence of an OH group or an NH group on(a) the melting and boiling points of the molecule? Explain.(b) the solubility of the molecule in polar solvents? Explain.

2. Identify all components of functional groups in the fol-lowing structural diagrams. Predict the solubility of eachsubstance in water.(a) CH3OH(b) CH3CHCHCH3(c) CH3CHO(d)

3. The compounds water, ammonia, and methane are formedwhen an oxygen atom, a nitrogen atom, and a carbon atomeach bonds with hydrogen atoms.(a) Write a formula for each of the three compounds.(b) Predict, with reference to electronegativities and inter-

molecular forces, the solubility of each of the com-pounds in the others.

(c) Of the three compounds, identify which are found orproduced by living organisms, and classify each com-pound as organic or inorganic. Justify your answer.

OH

CH3CH2CO


1.21.2HydrocarbonsWe will begin our study of organic families with a review of hydrocarbons, many ofwhich contain multiple bonds between carbon atoms, a functional group with charac-teristic properties.

Fossil fuels (Figure 1) contain mainly hydrocarbons: simple molecules of hydrogenand carbon that are the result of the breakdown of living organisms from long ago. Thesecompounds include the natural gas that is piped to our homes, the propane in tanks forbarbecues, and the gasoline for our cars. Hydrocarbons are classified by the kinds ofcarboncarbon bonds in their molecules. In alkanes, all carbons are bonded to otheratoms by single bonds, resulting in the maximum number of hydrogen atoms bonded toeach carbon atom. These molecules are thus called saturated hydrocarbons. Alkenes arehydrocarbons that contain one or more carboncarbon double bonds, and alkynes con-tain one or more carboncarbon triple bonds. These two groups are called unsaturatedhydrocarbons because they contain fewer than the maximum possible number of hydrogenatoms. Because alkenes and alkynes have multiple bonds, they react in characteristic ways.The multiple bond is the functional group of these two chemical families.

In all of these hydrocarbons, the carboncarbon backbone may form a straight chain,one or more branched chains, or a cyclic (ring) structure (Table 1). All of these mole-cules are included in a group called aliphatic hydrocarbons.

A hydrocarbon branch that is attached to the main structure of the molecule is calledan alkyl group. When methane is attached to the main chain of a molecule, it is calleda methyl group, CH3. An ethyl group is CH3CH2, the branch formed when ethanelinks to another chain.

hydrocarbon an organic compoundthat contains only carbon andhydrogen atoms in its molecularstructure

alkane a hydrocarbon with onlysingle bonds between carbon atoms

alkene a hydrocarbon that containsat least one carboncarbon doublebond; general formula, CnH2n

alkyne a hydrocarbon that containsat least one carboncarbon triplebond; general formula, CnH2n2

cyclic hydrocarbon a hydrocarbonwhose molecules have a closed ringstructure

aliphatic hydrocarbon a com-pound that has a structure based onstraight or branched chains or ringsof carbon atoms; does not includearomatic compounds such as ben-zene

alkyl group a hydrocarbon groupderived from an alkane by theremoval of a hydrogen atom; often asubstitution group or branch on anorganic molecule

Figure 1Crude oil is made up of a variety ofpotentially useful hydrocarbons.

Table 1 Examples of Hydrocarbons

Hydrocarbon Example Formula Spacefill Bond and anglesgroup diagram diagram

Aliphatic

alkane ethane CH3CH3

cyclohexane C6H12

alkene ethene CH2CH2

alkyne ethyne CHCH

Aromatic

benzene C6H6

120

12 Chapter 1 NEL

A fourth group of hydrocarbons with characteristic properties and structures is calledthe aromatic hydrocarbons. The simplest aromatic hydrocarbon is benzene; all othermembers of this family are derivatives of benzene. The formula for benzene is C6H6,and the six carbon atoms form a unique ring structure. Unlike cyclohexane, C6H12, thebenzene ring has a planar (flat) structure, and is unsaturated (Table 1). As we will learnlater in this chapter and in Chapter 10, the bonds in the benzene ring have properties inter-mediate between single bonds and double bonds; the common structural diagram forbenzene shows a hexagon with an inscribed circle, symbolizing the presence of doublebonds in unspecified locations within the six-carbon ring (Figure 2). The unique struc-ture and properties of compounds containing benzene rings have prompted their clas-sification as a broad organic family of their own. Named historically for the pleasantaromas of compounds such as oil of wintergreen, aromatic compounds include allorganic molecules that contain the benzene ring. All other hydrocarbons and theiroxygen or nitrogen derivatives that are not aromatic are called aliphatic compounds.

Nomenclature of HydrocarbonsBecause there are so many organic compounds, a systematic method of naming them isessential. In this book, we will use the IUPAC system of nomenclature, with additionalnonsystematic names that you may encounter in common usage. It is especially impor-tant to have a good grasp of the nomenclature of hydrocarbons, as the names of manyorganic molecules are based on those of hydrocarbon parent molecules.

AlkanesAll alkanes are named with the suffix -ane. The prefix in the name indicates the numberof carbon atoms in the longest straight chain in the molecule (Table 2). Thus a 5-Cstraight-chained alkane would be named pentane.

Any alkyl branches in the carbon chain are named with the prefix for the branch, fol-lowed by the suffix -yl. Thus, a branch that contains a 2-C chain is called an ethyl group.The name of a branched alkane must also indicate the point of attachment of the branch.This is accomplished by assigning numbers to each C atom of the parent alkane, and pointingout the location of the branch chain by the numeral of the C atom where the branching occurs.The naming system always uses the lowest numbers possible to denote a position on the chain.Finally, all numerals are separated by commas; numerals and letters are separated by hyphens;and names of branches and parent chains are not separated.

aromatic hydrocarbon a com-pound with a structure based onbenzene: a ring of six carbon atoms

IUPAC International Union of Pureand Applied Chemistry; the organi-zation that establishes the conven-tions used by chemists

Figure 2Benzene, C6H6, is colourless, flam-mable, toxic, and carcinogenic, andhas a pleasant odour. Its meltingpoint is 5.5C and its boiling point80.1C. It is widely used in the man-ufacture of plastics, dyes, syntheticrubber, and drugs.

Joined Benzene RingsLike other hydrocarbons, benzenerings can link together to form awide variety of compounds(Figure 3), many of which arequite smelly!

Figure 3(a) Naphthalene, C10H8, is a colour-

less solid with a pungent odour.Its melting point is 80C, and itsboiling point 218C. However, itsublimes on heating. It is themain component of mothballs,and is also used as an insecti-cide, in solvents, and in the syn-thesis of dyes.

(b) Anthracene, C14H10, is a colour-less solid with melting andboiling points of 218C and354C. It is less well known, butis also used in the synthesis ofdyes.

DID YOU KNOW ??

(a)

(b)

Table 2 Alkanes and Related Alkyl Groups

Prefix IUPAC name Formula Alkyl group Alkyl formula

meth- methane CH4(g) methyl- CH3eth- ethane C2H6(g) ethyl- C2H5prop- propane C3H8(g) propyl- C3H7but- butane C4H10(g) butyl- C4H9pent- pentane C5H12(l) pentyl- C5H11hex- hexane C6H14(l) hexyl- C6H13hept- heptane C7H16(l) heptyl- C7H15oct- octane C8H18(l) octyl- C8H17non- nonane C9H20(l) nonyl- C9H19dec- decane C10H22(l) decyl- C10H21


We will take a special look at naming propyl groups and butyl groups. When alkylgroups have three or more C atoms, they may be attached to a parent chain either attheir end C atom, or at one of the middle C atoms. For example, Figure 4 shows two pointsof attachment for a propyl group. The two arrangements are structural isomers of eachother, and are commonly known by their nonsystematic names. The prefix n- (normal)refers to a straight-chain alkyl group, the point of attachment being at an end C atom.The isomer of the n-propyl group is the isopropyl group. Figure 5 shows the commonnames for isomers of the butyl group; in this book, we will not concern ourselves withisomers of alkyl groups greater than 4 C atoms.

Section 1.2

isomer a compound with the samemolecular formula as another com-pound, but a different molecularstructure

CH3 CH CH3

Figure 4Two isomers of the propyl group.The coloured bond indicates wherethe group is attached to the largermolecule.

CH3 CH2 CH2 (a)

(b)

CH3 CH CH2 CH3

Figure 5Four isomers of the butyl group

C

CH3

CH3

CH3

CH2

CH3 CH CH3CH3 CH2 CH2 CH2(a) (b)

(c) (d)

isobutyl

n-butyl (normal butyl)

t-butyl (tertiary butyl)

s-butyl (secondary butyl)

isopropyl

n-propyl (normal propyl)

1. Write the IUPAC name for the chemical with the following structural diagram.

First, identify the longest carbon chain. Note that you may have to count along whatappear to be branches in the structural diagram to make sure you truly have the longestchain. In this case, the longest carbon chain is 6 C long. So the parent alkane is hexane.

Next, number the C atoms as shown.

In this case, there are several possible six-carbon chains. Choose the one that gives thelowest possible total of numbers identifying the location of the branches. Usually it is bestto start numbering with the end carbon that is closest to a branch. In this case, the firstbranch is on C 2. Notice that it makes no difference whether we choose C 1a or C 1b to bethe actual C 1.

Naming Alkanes SAMPLE problem

CH3

CH3 CH2 CH CH CH CH3

CH2

CH3

CH2 CH3

CH3

CH3 CH2 CH CH CH CH3

CH2

CH3

CH2 CH3

6

6 5 4 3 2 1a

5 1b

14 Chapter 1 NEL

Name each branch and identify its location on the parent chain. In this example, thereis a methyl group on C 2 and an ethyl group on each of C 3 and C 4. Thus the branchesare 2-methyl, 3-ethyl, and 4-ethyl.

To check that youve got the lowest total, try naming the structure from the other endsof the chain. If we had counted from either of the C 6 ends, we would arrive at 3-ethyl, 4-ethyl, and 5-methyla set of numbers with a higher total.

When the same alkyl group (e.g., ethyl) appears more than once, they are grouped asdi-, tri-, tetra-, etc. In this compound, the two ethyl groups are combined as 3,4-diethyl.

Finally, write the complete IUPAC name, following this format: (number indicating loca-tion)-(branch name)(parent chain). In this book, when more than one branch is present,the branches are listed in alphabetical order. (Note that other sources may list thebranches in order of complexity.) Alphabetically, ethyl comes before methyl. So the namebegins with the ethyl groups, followed by the methyl group, and ends with the parentalkane. Watch the use of commas and hyphens, and note that no punctuation is usedbetween the alkane name and the alkyl group that precedes it.

The IUPAC name for this compound is 3,4-diethyl-2-methylhexane.

2. Write the IUPAC name for the following hydrocarbon.

First, identify the longest carbon chain: 8 C atoms. So the molecule is an octane.Next, number the C atoms as shown.

If we start counting at C 1, the branch group attached to C 3 contains 3 C atoms, so it isa propyl group. However, the propyl group is attached to the parent chain at its middle Catom, not at an end C atom. This arrangement of the propyl group is called isopropyl(Figure 4(b)).

One possible name for this compound is 3-isopropyloctane.However, a different name results if we number this hydrocarbon from the top branch.

This shows a methyl group on C 2 and an ethyl group on C 3, giving the name 3-ethyl-2-methyloctane. Where more than one name is correct, we use the one thatincludes the lowest possible numerals.

The correct name of this compound is 3-ethyl-2-methyloctane.

3. Draw a structural diagram for 1,3-dimethylcyclopentane.

The parent alkane is cyclopentane. Start by drawing a ring of 5 C atoms single-bonded toeach other, in the shape of a pentagon.

Next, number the C atoms in the ring, starting anywhere in the ring.Then attach a methyl group to C 1 and another to C 3.Finally, add H atoms to the C atoms to complete the bonding and the diagram.

CH3 CH2 CH CH2 CH2 CH2 CH2 CH3

CH3 CH2 CH3


CH3 CH2 CH3

1 2 3 4 5 6 7 8


CH3 CH CH3

3 4 5 6 7 8

1 2

1CH

CH3

2CH25CH2

3CH CH34CH2


Section 1.2

ExampleWrite the IUPAC name for the following hydrocarbon.

SolutionThis alkane is 3,4,4-trimethylheptane.

CH3 CH2 CH C CH CH3

CH3

CH3 CH2

CH3

Step 1 Identify the longest carbon chain; note that structural diagrams can bedeceivingthe longest chain may travel through one or morebranches in the diagram.

Step 2 Number the carbon atoms, starting with the end that is closest to thebranch(es).

Step 3 Name each branch and identify its location on the parent chain by thenumber of the carbon at the point of attachment. Note that the namewith the lowest numerals for the branches is preferred. (This mayrequire restarting your count from the other end of the longest chain.)

Step 4 Write the complete IUPAC name, following this format: (number oflocation)-(branch name)(parent chain).

Step 5 When more than one branch is present, the branches are listed either inalphabetical order or in order of complexity; in this book, we will followthe alphabetical order.

Note: When naming cyclic hydrocarbons, the carbon atoms that form the ringstructure form the parent chain; the prefix cyclo- is added to the parenthydrocarbon name, and the naming of substituted groups is the same asfor noncyclic compounds.

Naming Branched AlkanesSUMMARY


1. Write IUPAC names for the following hydrocarbons.(a)

CH3 CH CH CH CH CH2 CH3

CH3 CH2

CH3

CH3CH3

4-ethyl-2,3,5-trimethylheptane

The structure of an organic mole-cule can be represented in manydifferent ways: some representa-tions give three-dimensional detail;others are simplified to show onlythe carbon backbone and func-tional groups. The following struc-tural diagrams all show the samemoleculepentanoic acidbut inslightly different ways.

LEARNING TIP

CH3 CH2 CH2 CH2 C OH

O

OH

O

(a)

(b)

(c)

(d)

Alkenes and AlkynesThe general rules for naming alkenes and alkynes are similar to those for alkanes, usingthe alkyl prefixes and ending with -ene or -yne respectively.

16 Chapter 1 NEL

(b)

(c)

(d)

2. Draw a structural diagram for each of the following hydrocarbons:(a) 3,3,5-trimethyloctane(b) 3,4-dimethyl-4-ethylheptane(c) 2-methyl-4-isopropylnonane(d) cyclobutane(e) 1,1-diethylcyclohexane

CH3 CH CH2 CH2 CH2 CH CH3

CH2 CH3 CH2 CH3

CH3 CH CH2 CH CH2 CH CH3

CH2CH3

CH3 CH2CH2CH3

CH

CH3

CH2

CHCH2

CH2CH2

CH3

1. Write the IUPAC name for the hydrocarbon whose structural diagram andball-and-stick model are shown.

First, find the longest C chain that includes the multiple bond. In this case, it is 4 C long,so the alkene is a butene.

Number the C atoms, beginning with the end closest to the double bond.The double bond is between C 1 and C 2, so the alkene is a 1-butene.

Next, identify any branches: A methyl group is attached to C 3, so the branch is 3-methyl.

Finally, write the name, following the conventions for hyphenation and punctuation.Since a number precedes the word butene, hyphens are inserted and the alkene is 3-methyl-1-butene.

Naming Alkenes and AlkynesSAMPLE problem

CH3 CH CH CH2

CH3

CH3 CH CH CH2

CH3

4

4

3 2 1


Section 1.2

2. Draw a structural diagram for 2-methyl-1,3-pentadiene.

First, draw and number a 5 C chain for the pentadiene.

Now insert the double bonds. The name diene tells us that there are two doublebonds, one starting at C 1 and another starting at C 3.

Draw a methyl group attached to C atom 2.

Finally, write in the remaining H atoms.

3. Write the IUPAC name for the compound whose structural diagram and ball-and-stick model are shown.

First, identify the ring structure, which contains 6 C atoms with one double bond. Theparent alkene is therefore cyclohexene.

Next, number the C atoms beginningwith one of the C atoms in the doublebond. The numbering system shouldresult in the attached group having thelowest possible number, which placesthe methyl group at C 3 .

The IUPAC name for this compound is 3-methylcyclohexene.

Example 1Draw a structural diagram for 3,3-dimethyl-1-butyne.

Solution

C C C C C1 2 3 4 5

C C C C C1 2 3 4 5

C C C C C1 2 3 4 5

CH3

CH2 C CH CH CH3

CH3

2

3

6

5

1

4CH3

CH3

CCCH

CH3

CH3

CH3

18 Chapter 1 NEL

Example 2Write the IUPAC name for the following compound.

SolutionThe compound is 3-isopropyl-1,3-hexadiene.

CH2 CH C CH CH2 CH3

CH3 CH CH3


3. Explain why no number is used in the names ethene and propene.

4. Write the IUPAC name and the common name for the compound in Figure 6.

5. Write IUPAC names for the compounds with the following structural diagrams:(a)

Figure 6When this compound combusts, it transfersenough heat to melt most metals.

Some alkenes and alkyneshave common names.

LEARNING TIP

IUPAC Commonname name

ethene ethylene

propene propylene

ethyne acetylene

Step 1. The parent chain must be an alkene or alkyne, and thus must containthe multiple bond.

Step 2. When numbering the C atoms in the parent chain, begin with the endclosest to the multiple bond.

Step 3. The location of the multiple bond is indicated by the number of the Catom that begins the multiple bond; for example, if a double bond isbetween the second and third C atoms of a pentene, it is named 2-pentene.

Step 4. The presence and location of multiple double bonds or triple bonds isindicated by the prefixes di-, tri-, etc.; for example, an octene withdouble bonds at the second, fourth, and sixth C atoms is named 2,4,6-octatriene.

Naming Alkenes and AlkynesSUMMARY

C

CH3 CH3

CH CH

CH2 CH3

CH3 CH2C


Aromatic HydrocarbonsIn naming simple aromatic compounds, we usually consider the benzene ring to be the parent molecule, with alkyl groups named as branches attached to the benzene.For example, if a methyl group is attached to a benzene ring, the molecule is calledmethylbenzene (Figure 7). Since the 6 C atoms of benzene are in a ring, with no begin-ning or end, we do not need to include a number when naming aromatic compoundsthat contain only one additional group.

When two or more groups are attached to the benzene ring, we do need to use a num-bering system to indicate the locations of the groups. We always number the C atoms sothat we have the lowest possible numbers for the points of attachment. Numbering mayproceed either clockwise or counterclockwise. As shown in the examples in Figure 8,we start numbering with one of the attached ethyl groups, then proceed in the directionthat is closest to the next ethyl group.

Section 1.2

(b)

(c)(d)

(e)

6. Draw structural diagrams for each of the following compounds:(a) 2-methyl-5-ethyl-2-heptene(b) 1,3,5-hexatriene(c) 3,4-dimethylcyclohexene(d) 1-butyne(e) 4-methyl-2-pentyne

CH

CH2

C CH2CH3 CH3

CH2 CH3

CH CH CH

CH2 CH2CH3

CH2 CH CH3

CH3

CH3

CHCH3CH CH2 CH CH CH2 CH CH2

C2H5

C2H51

2

3

6

5

4

C2H5

C2H5

1

2

3

6

5

4

2

C2H5

C2H5

1

3

6

5

4

(a) 1,2-diethylbenzene (b) 1,3-diethylbenzene (c) 1,4-diethylbenzeneFigure 8Three isomers of diethylbenzene

CH3

Figure 7Methylbenzene, commonly calledtoluene, is a colourless liquid that isinsoluble in water, but will dissolve inalcohol and other organic fluids. It isused as a solvent in glues and lac-quers and is toxic to humans. Toluenereacts with nitric acid to produce theexplosive trinitrotoluene (TNT).


Section 1.2

Solution(a) 1-ethyl-2,4-dimethylbenzene(b) 4-phenyl-3-propyl-1-hexene

1. If an alkyl group is attached to a benzene ring, the compound is named as analkylbenzene. Alternatively, the benzene ring may be considered as a branchof a large molecule; in this case, the benzene ring is called a phenyl group.

2. If more than one alkyl group is attached to a benzene ring, the groups arenumbered using the lowest numbers possible, starting with one of the addedgroups.

Naming Aromatic HydrocarbonsSUMMARY

Practice7. Write IUPAC names for the following hydrocarbons.

(a)

(b)

(c)

(d)

8. Draw structural diagrams for the following hydrocarbons:(a) 1,2,4-trimethylbenzene(b) 1-ethyl-2-methylbenzene(c) 3-phenylpentane(d) o-diethylbenzene(e) p-ethylmethylbenzene

CH3 CH2 CH CH CH3

C2H5

CH2 CH CH CH

CH3C2H5

CH C CH2 CH CH3

CH3

CH2CH2CH3

22 Chapter 1 NEL

Physical Properties of HydrocarbonsSince hydrocarbons contain only C and H atoms, two elements with very similar elec-tronegativities, bonds between C and H are relatively nonpolar. The main intermolec-ular interaction in hydrocarbons is van der Waals forces: the attraction of the electronsof one molecule for the nuclei of another molecule. Since these intermolecular forces areweak, the molecules are readily separated. The low boiling points and melting points ofthe smaller molecules are due to the fact that small molecules have fewer electrons andweaker van der Waals forces, compared with large molecules (Table 3). These differ-ences in boiling points of the components of petroleum enable the separation of thesecompounds in a process called fractional distillation. Hydrocarbons, being largely non-polar, generally have very low solubility in polar solvents such as water, which is whygasoline remains separate from water (Figure 10). This property of hydrocarbons makesthem good solvents for other nonpolar molecules.

Figure 10The nonpolar hydrocarbons in gaso-line are insoluble in water andremain in a separate phase.

fractional distillation the separationof components of petroleum by distil-lation, using differences in boilingpoints; also called fractionation

Table 3 Boiling Points of the First 10 Straight Alkanes

Formula Name b.p. (C)

CH4(g) methane 161

C2H6(g) ethane 89

C3H8(g) propane 44

C4H10(g) butane 0.5

C5H12(l) pentane 36

C6H14(l) hexane 68

C7H16(l) heptane 98

C8H18(l) octane 125

C9H20(l) nonane 151

C10H22(l) decane 174


1. Draw a structural diagram for each hydrocarbon:(a) 2-ethyloctane(b) 2-ethyl-3-isepropylnonane(c) methylcyclopentane(d) 3-hexyne(e) 3-methyl-1,5-heptadiene(f) 1,2,4-trimethylbenzene(g) 4-s-butyloctane(h) 2-phenylpropane(i) 3-methyl-2-pentene(j) n-propylbenzene(k) p-diethylbenzene(l) 1, 3-dimethylcyclohexane

2. For each of the following names, determine if it is a correctname for an organic compound. Give reasons for youranswer, including a correct name.(a) 2-dimethylhexane(b) 3-methyl-1-pentyne(c) 2,4-dimethylheptene(d) 3,3-ethylpentane(e) 3,4-dimethylhexane(f) 3,3-dimethylcyclohexene(g) 2-ethyl-2-methylpropane(h) 2,2-dimethyl-1-butene(i) 1-methyl-2-ethylpentane(j) 2-methylbenzene(k) 1,5-dimethylbenzene(l) 3,3-dimethylbutane


Section 1.2

3. Write correct IUPAC names for the following structures.(a)

(b)

(c)

(d)

(e)

4. Draw a structural diagram for each of the following com-pounds, and write the IUPAC name for each:(a) ethylene(b) propylene(c) acetylene(d) toluene, the toxic solvent used in many glues(e) the o-, m-, and p- isomers of xylene (dimethylben-

zene), used in the synthesis of other organic com-pounds such as dyes

Making Connections

5. (a) Use the information in Table 3 to plot a graph showingthe relationship between the number of carbon atomsand the boiling points of the alkanes. Describe andpropose an explanation for the relationship you discover.

(b) Research a use for each of the first 10 alkanes, andsuggest why each is appropriate for this use.

CH3CH2CHCHCH3

CH3

CH2CH3

CH2CH3

CH3CHCH3

CH3CCH CH2

CH3CHCH2CH3

GO www.science.nelson.com

CH3CH2CH CHCHCH CHCH3

CH3CHCH3CH2CH3

CH3

24 Chapter 1 NEL

1.31.3 Reactions of HydrocarbonsAll hydrocarbons readily burn in air to give carbon dioxide and water, with the releaseof large amounts of energy (Figure 1); this chemical reaction accounts for the exten-sive use of hydrocarbons as fuel for our homes, cars, and jet engines. In other chemicalreactions, alkanes are generally less reactive than alkenes and alkynes, a result of thepresence of more reactive double and triple bonds in the latter. Aromatic compounds,with their benzene rings, are generally more reactive than the alkanes, and less reactivethan the alkenes and alkynes. In this section, we will examine this trend in the chemicalreactivity of hydrocarbons.

When we are representing reactions involving large molecules, it is often simpler to usea form of shorthand to represent the various functional groups. Table 1 shows some ofthe commonly used symbols. For example, R represents any alkyl group attachedto a benzene ring, and RX represents any alkyl group attached to any halogen atom.

Reactions of AlkanesThe characteristic reactions of saturated and unsaturated hydrocarbons can be explainedby the types of carboncarbon bonds in saturated and unsaturated hydrocarbons.Single covalent bonds between carbon atoms are relatively difficult to break, and thusalkanes are rather unreactive. They do undergo combustion reactions if ignited in air,making them useful fuels. Indeed, all hydrocarbons are capable of combustion to pro-duce carbon dioxide and water. The reaction of propane gas, commonly used in gas bar-becues, is shown below:

C3H8(g) 5 O2(g) 3 CO2(g) 4 H2O(g)

While the CC bonds in alkanes are difficult to break, the hydrogen atoms may be sub-stituted by a halogen atom in a substitution reaction with F2, Cl2, or Br2. Reactions withF2 are vigorous, but Cl2 and Br2 require heat or ultraviolet light to first dissociate thehalogen molecules before the reaction will proceed. In each case, the product formed isa halogenated alkane; as the halogen atom(s) act as a functional group, halogenatedalkanes are also referred to as an organic family called alkyl halides.

In the reaction of ethane with bromine, the orange colour of the bromine slowly dis-appears, and the presence of HBr(g) is indicated by a colour change of moist litmus paperfrom blue to red. A balanced equation for the reaction is shown below.

24 Chapter 1 NEL

Figure 1Hydrocarbons are found as solids,liquids, and gases, all of which burnto produce carbon dioxide andwater, and large amounts of lightand heat energy.

Table 1 Examples of Symbols Representing Functional Groups

Group Symbol

alkyl group R, R, R, etc. (R, R-prime, R-double prime)

halogen atom X

phenyl group

combustion reaction the reactionof a substance with oxygen, pro-ducing oxides and energy

substitution reaction a reaction inwhich a hydrogen atom is replacedby another atom or group of atoms;reaction of alkanes or aromaticswith halogens to produce organichalides and hydrogen halides

alkyl halide an alkane in which oneor more of the hydrogen atoms havebeen replaced with a halogen atomas a result of a substitution reaction

H

H

C C H(g) + Br2( l)

H

H

H

H

H

C C H( l) + HBr( l)

Br

H

H

bromoethane,(ethyl bromide)

heat or UV light (substitutionreaction)

Preparation of Ethyne (p. 84)How close does the actual yieldcome to the theoretical yield in thereaction between calcium carbideand water?

LAB EXERCISE 1.3.1


As the reaction proceeds, the concentration of bromoethane increases and brominereacts with it again, leading to the substitution of another of its hydrogen atoms, forming1,2-dibromoethane.

Additional bromines may be added, resulting in a mixture of brominated products that(because of differences in physical properties) can be separated by procedures such as dis-tillation.

Reactions of Alkenes and AlkynesAlkenes and alkynes exhibit much greater chemical reactivity than alkanes. For example,the reaction of these unsaturated hydrocarbons with bromine is fast, and will occur atroom temperature (Figure 2). (Recall that the bromination of alkanes requires heat orUV light.) This increased reactivity is attributed to the presence of the double and triplebonds. This characteristic reaction of alkenes and alkynes is called an addition reac-tion as atoms are added to the molecule with no loss of hydrogen atoms.

Alkenes and alkynes can undergo addition reactions not only with halogens, but alsowith hydrogen, hydrogen halides, and water, given the appropriate conditions. Examplesof these reactions are shown below.

Halogenation (with Br2 or Cl2)

Hydrogenation (with H2)

Hydrohalogenation (with hydrogen halides)

Section 1.3

H

H

C C H(g) + Br2(g)

Br

H

H

1,2-dibromoethane

Br

H

C C H(l) + HBr(g)

Br

H

H

(substitution reaction)

heat or UV light

Figure 2The reaction of cyclohexene andbromine water, Br2(aq), is rapid,forming a layer of brominated cyclohexane (clear).

addition reaction a reaction ofalkenes and alkynes in which a molecule, such as hydrogen or ahalogen, is added to a double ortriple bond

H

C C H + Brz(g)

H

H

1,2-dibromoethane

Br

H

C C H

Br

H

H (addition reaction)

ethene

roomtemperature

C C H + 2Hz(g)H

ethane

H

H

C C H

H

H


ethyne

catalyst

heat, pressure

C CH CH3 + HBr(g)H

2-bromopropane

H

C

HH

CH CH3

Br


propene

roomtemperature

Table 2 Prefixes for Functional Groups

Functional group Prefix

F fluoro

Cl chloro

Br bromo

I iodo

OH hydroxy

NO2 nitro

NH2 amino

MargarineVegetable oils consist of moleculeswith long hydrocarbon chains con-taining many double bonds; theseoils are called polyunsaturated.The oils are hardened by under-going hydrogenation reactions toproduce more saturated mole-cules, similar to those in animalfats such as lard.

DID YOU KNOW ??

26 Chapter 1 NEL

Hydration (with H2O)

Markovnikovs RuleWhen molecules such as H2, consisting of two identical atoms, are added to a doublebond, only one possible product is formed; in other words, addition of identical atomsto either side of the double bond results in identical products.

When molecules of nonidentical atoms are added, however, two different products aretheoretically possible. For example, when HBr is added to propene, the H may add to Catom 1, or it may add to C 2; two different products are possible, as shown below.

Experiments show that, in fact, only one main product is formed. The product can bepredicted by a rule known as Markovnikovs rule, first stated by Russian chemist V. V.Markovnikov (18381904).

As illustrated in the reaction of propene above, the first C atom has two attached Hatoms, while the second C atom has only one attached H atom. Therefore, the rich C1atom gets richer by gaining the additional H atom; the Br atom attaches to the middleC atom. The main product formed in this reaction is 2-bromopropane.

CH CH CH3 + HOHH2-hydroxypropane (an alcohol)

H

CH CH3

OH

H2C (addition reaction)propene

H2SO4catalyst

CH CH CH3 + HBrH

2-bromopropane (main product)

H

CH CH3

Br

H2C

Br

CH CH3

H

H2C

propene 1-bromopropane

or

Markovnikovs RuleWhen a hydrogen halide or water is added to an alkene oralkyne, the hydrogen atom bonds to the carbon atom withinthe double bond that already has more hydrogen atoms. Thisrule may be remembered simply as the rich get richer.

What compound will be produced when water reacts with 2-methyl-1-pentene?

First, write the structural formula for 2-methyl-1-pentene.

Next, identify the C atom within the double bond that has more H atoms attached.Since carbon 1 has two H atoms attached, and carbon 2 has no H atoms attached, the H atom in the HOH adds to carbon 1, and the OH group adds to carbon 2.

We can now predict the product of the reaction.

The compound produced is 2-hydroxy-2-methylpentane.

Predicting Products of Addition ReactionsSAMPLE problem

CH3

CH2CH3CH2CH2C5 4 3 2 1

CH3


+ HOH

CH3


OH H


Section 1.3

ExampleDraw structural diagrams to represent an addition reaction of an alkene to produce 2-chlorobutane.

Solution


1. What compounds will be produced in the following addition reactions?(a)

(b)

(c)

(d)

H2C CHCH2CH3 + HCl H2C CHCH2CH3

H Cl

1-butene

CH3CH CCH2CH3 H2

CH2CH3

Pt catalyst

500C

CH3CH CCH2CH3 HBr

CH3

CH3CH2CHCH CH2 H2O

CH2CH3

H2SO4

Cl2

Synthesis: Choosing Where to StartAddition reactions are important reactions that are often used in the synthesis of com-plex organic molecules. Careful selection of an alkene as starting material allows us tostrategically place functional groups such as a halogen or a hydroxyl group (OH) indesired positions on a carbon chain. As we will see later in this chapter, the products ofthese addition reactions can in turn take part in further reactions to synthesize otherorganic compounds, such as vinegars and fragrances.


2. Explain the phrase "the rich get richer" as it applies to Markovnikovs rule.

3. Draw structural diagrams to represent addition reactions to produce each of the following compounds:(a) 2,3-dichlorohexane(b) 2-bromobutane(c) 2-hydroxy-3-methylpentane(d) 3-hydroxy-3-methylpentane

28 Chapter 1 NEL

Reactions of Aromatic HydrocarbonsSince aromatic hydrocarbons are unsaturated, one might expect that they would readilyundergo addition reactions, as alkenes do. Experiments show, however, that the ben-zene ring does not undergo addition reactions except under extreme conditions of tem-perature and pressure. They are less reactive than alkenes.

Aromatic hydrocarbons do undergo substitution reactions, however, as alkanes do.In fact, the hydrogen atoms in the benzene ring are more easily replaced than those inalkanes. When benzene is reacted with bromine in the presence of a catalyst, bro-mobenzene is produced.

Overall, the reactivity of aromatic hydrocarbons appears to be intermediate betweenthat of alkanes and alkenes.

(a) cyclohexane + Br2 bromocyclohexane

(b) benzene + Br2 bromobenzene

(c) cyclohexene + Br2 bromocyclohexane

Further reaction of bromobenzene with Br2 results in the substitution of another Bron the ring. In theory, this second Br atom may substitute for an H atom on any of theother C atoms, resulting in three possible isomers of dibromobenzene.

In practice, the 1,3 isomer appears to be favoured.

Br2 HBr

Br

cyclohexane bromocyclohexane

(substitution reaction)heat UV

Br2

Br

Br

roomtemperature

cyclohexene 1,2-dibromocyclohexane

(addition reaction)

Br2

Br

BrBr

1, 2-dibromobenzene

and/or and/or

Br

1, 3-dibromobenzene

Br

Br

1, 4-dibromobenzene

Br

Br2 HBr

BrFeBr3

benzene bromobenzene

(substitution reaction;addition does not occur)


The relatively low reactivity of aromatic hydrocarbons indicates that the benzenestructure is particularly stable. It seems that the bonds in a benzene ring are unlike thedouble or triple bonds in alkenes or alkynes. In 1865, the German architect and chemistFriedrich August Kekul (18291896) proposed a cyclic structure for benzene, C6H6.With 6 C atoms in the ring, and one H atom on each C atom, it appears that there mightbe 3 double bonds within the ring, each alternating with a single bond. As carboncarbondouble bonds are shorter than single bonds, we would predict that the bonds in thebenzene ring would be of different lengths. Experimental evidence, however, shows oth-erwise. The technique of X-ray diffraction indicates that all the CC bonds in benzeneare identical in length and in strength (intermediate between that of single and doublebonds). Therefore, rather than having 3 double bonds and 3 single bonds, an accept-able model for benzene would require that the valence electrons be shared equally amongall 6 C atoms, making 6 identical bonds. A model of benzene is shown in Figure 3. In thismodel, the 18 valence electrons are shared equally, in a delocalized arrangement; there isno specific location for the shared electrons, and all bond strengths are intermediatebetween that of single and double bonds. This explains why benzene rings do not undergoaddition reactions as double bonds do, and why they do undergo substitution reactionsas single bonds do, and do so more readily. In Chapter 4, you will examine in more detailthe unique bonding that is present in the benzene ring.

In another substitution reaction, benzene reacts with nitric acid in the presence ofH2SO4 to form nitrobenzene. Benzene also reacts with alkyl halides (RX) in the pres-ence of an aluminum halide catalyst (AlX3); the alkyl group attaches to the benzenering, displacing an H atom on the ring. These products can undergo further reactions,enabling the design and synthesis of aromatic compounds with desired groups attachedin specific positions.

Section 1.3

HNO3 H2O (substitution reaction)

nitrobenzene

NO2H2SO4

CH3CH2Cl HCl (substitution reaction)

ethylbenzene

CH2CH3AlCl3

Figure 3Kekul wrote the following diaryentry about a dream he had, inwhich he gained a clue to the struc-ture of benzene: Again the atomsgambolled before my eyes. This timethe smaller groups kept modestly tothe background. My minds eyes,rendered more acute by repeatedvisions of a similar kind, could nowdistinguish larger structures, of var-ious shapes; long rows, sometimesmore closely fitted together; alltwining and twisting in snakelikemotion. But look! What was that?One of the snakes grabbed its owntail, and the form whirled mockinglybefore my eyes. As if struck by light-ning I awoke; ... I spent the rest ofthe night in working out the conse-quences of the hypothesis.... If welearn to dream we shall perhapsdiscover the truth.

Predict the product or products formed when benzene is reacted with 2-chlorobutane, in the presence of a catalyst (AlCl3). Draw structural diagrams ofthe reactants and products.

The methyl group of chloromethane substitutes for one of the H atoms on the benzene ring,forming methylbenzene and releasing the chloride to react with the displaced hydrogen.

The products formed are methylbenzene (toluene) and hydrogen chloride.

Predicting Reactions of Aromatic Hydrocarbons SAMPLE problem

+ C1 C H + HCl

H

H

CH3

30 Chapter 1 NEL

ExampleDraw balanced chemical equations (including structural diagrams) to represent a seriesof reactions that would take place to synthesize ethylbenzene from benzene and ethene.Classify each reaction.

SolutionReaction 1: Halogenation (by addition) of ethene by hydrogen chloride

Reaction 2: Halogenation (by substitution) of benzene by chloroethane

H

C C H + H

H

H

chloroethane

H

H

C C H

H

H

ethene

Cl

Cl

H

+ H C C

H

H

H H

H

C C H + HCl

H

H

Cl


4. Predict the product or products formed in each of the following reactions:(a) (b)

5. Propose a reaction series that would produce 2-phenylbutane, starting with ben-zene and 1-butene as reactants.

6. Which of the terms addition, substitution, or halogenation describes the reac-tion between benzene and bromine? Explain.

7. Describe the bonding structure in benzene, and explain the experimental evidencein support of this structure.

Cl2 HNO3

NO2H2SO4

All hydrocarbons undergo combustion reactions with oxygen to produce carbondioxide and water.

Alkanes Primarily undergo substitution reactions, with heat or UV light:

with halogens or hydrogen halides: halogenationwith nitric acid

Reactions of HydrocarbonsSUMMARY


1. Write a balanced equation for each of the following types ofreactions of acetylene:(a) addition (c) halogenation(b) hydrogenation (d) hydration

2. Classify each of the following reactions as one of the fol-lowing types: addition, substitution, hydrogenation, halo-genation, or combustion. Write the names and thestructures for all reactants and products.(a) methyl-2-butene hydrogen (b) ethyne Cl2 (c)(d)

(e)

3. Classify and write structural formula equations for the fol-lowing organic reactions:

(a) 3-hexene water (b) 2-butene hydrogen butane(c) 4,4-dimethyl-2-pentyne hydrogen

2,2-dimethylpentane(d) methylbenzene oxygen carbon dioxide water(e) 2-butene 3-methylpentane

Applying Inquiry Skills

4. To make each of the following products, select the reac-tants and describe the experimental conditions needed.(a) 2-hydroxypropane(b) 1, 3-dichlorocyclohexane from cyclohexane(c) 2-methyl-2-hydroxypentane from an alkene(d) chlorobenzene

Making Connections

5. If a certain volume of propane gas at SATP were completelycombusted in oxygen, would the volume of gaseousproduct formed be greater or smaller than that of the reactant? By how much?

6. From your knowledge of intermolecular attractions, whichof these organic compounds2-chlorononane, 2-hydroxy-nonane, or nonanewould be the most effective solvent forremoving oil stains? Give reasons foryour answer.

7. TNT is an explosive with a colourfulhistory (Figure 5). Research andreport on who discovered it, and itsdevelopment, synthesis, uses, andmisuses.


Section 1.3

CH3 CH3 H2 (excess)C C

CH2 CH2

C2H5

CH3

CH3

CH3 OCH C O

C2H5

CH

Figure 5


Alkenes and Alkynes Primarily undergo addition reactions:

with H2: hydrogenationwith halogens or hydrogen halides: halogenationwith water: hydration

Aromatics Primarily undergo substitution reactions:

with X2: halogenation, Xwith HNO3: nitration, NO2with RX: alkylation, R

Do not undergo addition reactions.

H2SO4

32 Chapter 1 NEL

1.41.4 Organic HalidesOrganic halides are a group of compounds that includes many common products suchas Freons (chlorofluorocarbons, CFCs) used in refrigerators and air conditioners, andTeflon (polytetrafluoroethene), the nonstick coating used in cookware and labware.

While we use some organic halides in our everyday lives, many others are toxic and someare also carcinogenic, so their benefits must be balanced against potential hazards. Twosuch compounds, the insecticide DDT (dichlorodiphenyltrichloroethane) and the PCBs(polychlorinated biphenyls) used in electrical transformers, have been banned becauseof public concern about toxicity.

In Section 1.3 you learned that when H atoms in an alkane are replaced by halogenatoms, the resulting organic halide is more specifically referred to as an alkyl halide.

Naming Organic HalidesWhen naming organic halides, consider the halogen atom as an attachment on the parenthydrocarbon. The halogen name is shortened to fluoro-, chloro-, bromo-, or iodo-. Forexample, the structure shown below is 1,2-dichloroethane, indicating an ethane mole-cule substituted with a chlorine atom on carbon 1 and a chlorine atom on carbon 2.

32 Chapter 1 NEL

organic halide a compound ofcarbon and hydrogen in which oneor more hydrogen atoms have beenreplaced by halogen atoms

H

H C C

H

H

1,2-dichloroethane

Cl Cl

Draw a structural diagram for 2,2,5-tribromo-5-methylhexane.

First, draw and number the parent alkane chain, the hexane:

Next, add two Br atoms to carbon 2, one Br atom to carbon 5, and a methyl group tocarbon 5.

Drawing and Naming Organic HalidesSAMPLE problem

C1

C2

C3

C4

C5

C6

C1

C2

C3

C4

C5

C6

Br

CH3

Br

Br

1 2 3 4 5 6

Br

CH3

Br

Br

CH3CCH2CH2CCH3


Properties of Organic HalidesThe presence of the halogen atom on a hydrocarbon chain or ring renders the moleculemore polar. This is because halogens are more electronegative than C and H atoms, andso carbonhalogen bonds are more polar than CH bonds. The increased polarity of alkylhalides increases the strength of the intermolecular forces. Thus alkyl halides have higherboiling points than the corresponding hydrocarbons. Because like dissolves like, theincreased polarity also makes them more soluble in polar solvents than hydrocarbons ofsimilar size.

When organic halides are formed from halogenation of hydrocarbons, the productobtained is often a mixture of halogenated compounds. These compounds may con-tain 1, 2, 3, or more halogens per molecule, reflecting intermediate compounds that canbe further halogenated. The molecules that contain more halogen atoms are usually

Section 1.4

Finally, complete the bonding by adding H atoms to the C atoms.

Example 1Write the IUPAC name for CH3CH2CH2CH(Cl)CH2CH(Br)CH3.

SolutionThis compound is 2-bromo-4-chloroheptane.

Example 2Draw a structural diagram of 1,2-dichlorobenzene.

Solution

Cl

Cl


1. Draw structural diagrams for each of the following alkyl halides:(a) 1,2-dichloroethane (solvent for rubber)(b) tetrafluoroethene (used in the manufacture of Teflon)(c) 1,2-dichloro-1,1,2,2-tetrafluoroethane (refrigerant)(d) 1,4-dichlorobenzene (moth repellent)

2. Write IUPAC names for each of the formulas given. (a) CHI3 (antiseptic)(b)

(c) CH2Cl2 (paint remover)(d) CH2Br CHBr CH2Br (soil fumigant)

CH2 C

(insecticide)

CH3

CH2 Cl

34 Chapter 1 NEL

more polar than the less halogenated molecules, and thus have higher boiling points(Table 1). This difference in boiling points conveniently enables us to separate the com-ponents of a mixture by procedures such as fractional distillation.

The Cost of Air ConditioningThe cost of a new car with air conditioning includes the price of the unit plus an addi-tional air-conditioner tax. On top of that, there is another, less obvious, cost: possibleenvironmental damage. Let us take a look at how organic chemistry can be used to solve

some problems, and how sometimes new problems are created alongthe way.

In the late 1800s, refrigerators were cooled using toxic gases such asammonia, methyl chloride, and sulfur dioxide. When several fatal acci-dents occurred in the 1920s as a result of leaked coolant, the searchbegan for a safer refrigerant. In 1930 the DuPont company manufacturedFreon, a chlorofluorocarbon, CF2Cl2(g), also called CFC-12. (Industrialchemists sometimes name Freons using a non-SI system.) As it wasinert, it was considered very safe and its use spread to aerosol sprays,paints, and many other applications.

In the 1970s, large ozone holes were detected in the upper atmos-phere, particularly over the polar regions. It appears that although CFCsare inert in the lower atmosphere, they are reactive in the upper atmos-phere. In the presence of UV light, CFC moleculesincluding Freondecompose, releasing highly reactive chlorine atoms.

The chlorine destroys the ozone molecules in the stratosphere, leaving us unprotectedfrom harmful UV radiation (Figure 1). You may have learned about these reactions ina previous chemistry course.

Automobile air conditioners use over one-third of the total amount of Freon inCanada, and about 10% of this total is released into the atmosphere each year. Hence thesearch is on again to find a new chemical to meet the demand for inexpensive air-conditioning systems, and to minimize environmental damage. Two types of chemicalshave been developed as substitute refrigerants: the hydrochlorofluorocarbons (HCFCs),and the hydrofluorocarbons (HFCs). These molecules differ from CFCs in that theycontain hydrogen atoms in addition to carbon and halogen atoms. The H atoms reactwith hydroxyl groups in the atmosphere, decomposing the molecules. Since the HCFCsand HFCs readily decompose, they have less time to cause damage to the ozone layer. Notethat HCFCs still contain chlorine, the culprit in ozone depletion; HFCs contain no chlo-rine and so are the preferred substitute for CFCs. These molecules are more readilydecomposed in the lower atmosphere and thus have less time to cause damage. However,they do release carbon dioxide, a major greenhouse gas, upon decomposition.

The most commonly used coolant now is HFC-134a. Since 1995, it has been used inall new automobile air conditioners. In 2001, the Ontario government introduced leg-islation requiring that all old units, when refilling is needed, be adapted to use one of thenew alternative refrigerants.

Table 1 Boiling Points of Some Hydrocarbons and Corresponding Organic Halides

Hydrocarbon Boiling point (C) Alkyl halide Boiling point (C)

CH4 164 CH3Cl 24

C2H6 89 C2H5Cl 12

C3H8 42 C3H7Cl 46

C4H10 0.5 C4H9Cl 78

Figure 1An ozone hole (blue) forms overthe Antarctic every spring(September and October).


Preparing Organic HalidesAlkyl halides are produced in halogenation reactions with hydrocarbons, as we learnedin Section 1.3. Alkenes and alkynes readily add halogens or hydrogen halides to theirdouble and triple bonds. Recall also that Markovnikovs rule of the rich get richerapplies when hydrogen halides are reactants, and must be considered in designing the syn-thesis of specific alkyl halides. These alkyl halides can then be transformed into otherorganic compounds.

An example of the halogenation of an alkyne is shown below for a review of the reac-tions that produce alkyl halides. These reactions readily take place at room temperature.

Section 1.4


3. Create a flow chart outlining the effects of an accidental leak of refrigerant from acars air conditioner. Include chemical equations wherever possible.

4. Draw a time line showing the use and effects of various refrigerants over the last 150years.

5. (a) Write chemical equations predicting the decomposition of HCFCs and HFCs.(b) Why might HCFCs and HFCs decompose more quickly than CFCs?(c) Why might this make them less damaging than CFCs?

Role Play: Can We Afford Air Conditioning?When a car manufacturer is planning to develop a new model,all aspects of the vehicle are reconsidered. Government regula-tions prohibit the manufacture of new vehicles with air-condi-tioning units that use CFCs. Alternative coolants have beendeveloped, and now most manufacturers use HFC-134a.However, HFCs are greenhouses gases and so, if released, arelikely to be contributors to global warming. Imagine that a com-mittee is set up to decide whether the next new model shouldhave air conditioning using HFC-134a, or no air-conditioningunit at all. Committee members include: a union representativefor the production-line workers; the local MP; an environmen-talist; a reporter from a drivers magazine; a physician; a repre-sentative from the Canadian Automobile Association; anadvertising executive; shareholders in the car company.

(a) Costs can be measured in many ways: financial, social,environmental, political, etc. Choose one way of

assessing cost and collect and sort information to helpyou decide whether the costs of automobile air condi-tioners are justified.

(b) Select a role for yourselfsomeone who would be con-cerned about the kinds of costs that you haveresearched. Consider how this person might feel aboutthe issue of air conditioning.

(c) Role-play the meeting, with everyone taking a turn toput forward his/her position on whether the new carmodel should have air conditioning.

(d) After the meeting, discuss and summarize the mostimportant points made. If possible, come to a consensusabout the issue.

Define the Issue Identify Alternatives ResearchAnalyze the Issue Defend the Position Evaluate

Decision-Making SkillsEXPLORE an issue


H Cethyne

Br

C H + Br Br H C C H

Br

bromine 1,2-dibromoethene+

(a)

36 Chapter 1 NEL

If we wanted to produce a halide of a benzene ring, we would need to arrange a sub-stitution reaction with a halogen. The following example illustrates the chlorination ofbenzene in the presence of a catalyst. Further substitution can occur in the benzene ringuntil all hydrogen atoms are replaced by halogen atoms.

Preparing Alkenes from Alkyl Halides: Elimination ReactionsAlkyl halides can eliminate a hydrogen and a halide ion from adjacent carbon atoms,forming a double bond in their place, thereby becoming an alkene. The presence of ahydroxide ion is required, as shown in the example below. This type of reaction, in whichatoms or ions are removed from a molecule, is called an elimination reaction. Eliminationreactions of alkyl halides are the most commonly used method of preparing alkenes.

H C

Br

C H + Br Br H C C H

Br

bromine1,2-dibromoethene +Br Br

1,1,2,2-tetrabromoethane

Br Br(b)

H

Cl

Cl Cl ClFeCl3

benzene hydrogen chloridechlorine chlorobenzene

Br

H C C

H

H

HH

2-bromopropaneH

C

H

+

hydroxide ion+

OH

propene water bromide ion++

H C C H

HH

H

C

H

H O

H

Br+ +

elimination reaction a type oforganic reaction that results in theloss of a small molecule from alarger molecule; e.g., the removal ofH2 from an alkane

Mustard GasMustard gas is a toxic alkyl halidethat was used as a chemicalweapon in World War I. When thiscompound is inhaled, it reacts rap-idly with water molecules in thelungs, releasing HCl. The high concentrations of hydrochloric aciddestroy lung tissue, leading todeath. Mustard gas was banned inthe 1980s as a result of internationaltreaties, but nevertheless has beenused since.

DID YOU KNOW ??

ClCH2 CH2 S CH2 CH2Cl

Learning TipSeveral letter symbols are com-monly used in general formulasto represent constituents oforganic compounds:R represents any alkyl groupR, R, etc. (R-prime, R-doubleprime) represent any alkylgroup different from other RsX represents any halogen atom represents a phenyl group

LEARNING TIP

Functional group: RX

Preparation:

alkenes and alkynes organic halidesaddition reactions with halogens or hydrogen halides

alkanes and aromatics organic halidessubstitution reactions with halogens or hydrogen halides

Pathway to other groups:

alkyl halides alkeneselimination reactions, removing hydrogen and halide ions

Organic HalidesSUMMARY


Section 1.4


6. Classify the following as substitution or addition reactions. Predict all possible prod-ucts for the initial reaction only. Complete the word equation and the structural dia-gram equation in each case. You need not balance the equations.(a) trichloromethane chlorine (b) propene bromine (c) ethylene hydrogen iodide (d) ethane chlorine (e)(f)

(g)

Extension

7. Why are some organic halides toxic while others are not? And why are some organ-isms affected more than others? Use the Internet to find out, using the following keywords in your search: bioaccumulation; fat soluble; food chain. Report on your findingsin a short article for a popular science magazine or web site.


1. Draw structural diagrams to represent the elimination reac-tion of 2-chloropentane to form an alkene. Include reactants,reaction conditions, and all possible products and theirIUPAC names.

2. Classify and write structural formula equations for the fol-lowing organic reactions:(a) propane chlorine

1-chloropropane 2-chloropropane hydrogen chloride

(b) propene bromine 1,2-dibromopropane(c) benzene iodine iodobenzene hydrogen iodide

Applying Inquiry Skills

3. The synthesis of an organic compound typically involves aseries of reactions, for example, some substitutions andsome additions.(a) Plan a reaction beginning with a hydrocarbon to pre-

pare 1,1,2-trichloroethane.(b) What experimental complications might arise in

attempting the reactions suggested in part (a)?

Making Connections

4. Research examples of the use of organic chemistry toaddress health, safety, or environmental problems, and

write a report or present one such case study. Examples oftopics include: leaded and unleaded gasoline, use of sol-vents in dry cleaning, use of aerosol propellants, and use ofpesticides and fertilizers.

5. Why was mustard gas such an effective weapon, bothduring World War 1 and more recently? Research its prop-erties and effects, and what defences have been developedagainst it.

6. Shortly after the connection was made between the holein the ozone layer and the release of chlorofluorocarbons,many manufacturers stopped using CFCs as propellants inaerosol cans.(a) Research what alternatives were developed, and the

effectiveness of each in the marketplace. Are the alter-natives still in use? Have any of them been found tocause problems?

(b) Design a product (one that must be sprayed underpressure) and its packaging. Plan a marketing strategythat highlights the way in which your product issprayed from the container.

Cl C C Cl F F (excess)

H C C C C

H H H H

ClH H

H H

Cl Cl

Cl




38 Chapter 1 NEL38 Chapter 1 NEL

1.51.5 Alcohols and EthersAlcohols and ethers are structurally similar in that they are essentially water moleculeswith substituted alkyl groups. In alcohols, one of the two H atoms in H2O is replacedby an alkyl group; in ethers, both H atoms are replaced by alkyl groups. The molecularmodels in Figure 1 show water, the simplest alcohol, and the simplest ether. The prop-erties of these compounds are related to the effects of the polar hydroxyl groups (OH)and the nonpolar alkyl groups.

AlcoholsThe alcohol in wine and beer is more correctly called ethanol. It is formed by yeast, afungus that derives its energy from breaking down sugars, producing carbon dioxideand ethanol as waste products. Once the concentration of ethanol reaches a critical level,the yeast cannot survive and fermentation ceases. The alcohol content in wine is there-fore limited to about 13% (26 proof).

Other alcohols that are produced by living organisms include cholesterol and retinol,commonly known as vitamin A.

While ethanol is not as toxic as other alcohols, it is recognized as a central nervoussystem depressant and a narcotic poison. Ethanol can be purchased in alcoholic bever-ages, the only safe form to consume. The ethanol commonly used in science labora-tories is not intended for drinking and is purposely mixed with methanol, benzene, orother toxic materials in order to make it unpalatable.

Naming AlcoholsIn the IUPAC system of naming alcohols, the OH functional group is named -ol, andis added to the prefix of the parent alkane. As before, the parent alkane is the longestcarbon chain to which an OH group is attached. For example, the simplest alcohol,with one OH group attached to methane, is named methanol. It is highly toxic andingesting even small quantities can lead to blindness and death. The alcohol with twocarbon atoms is ethanol, the active ingredient in alcoholic beverages. It is an importantsynthetic organic chemical, used also as a solvent in lacquers, varnishes, perfumes, andflavourings, and is a raw material in the synthesis of other organic compounds.

38 Chapter 1 NEL

alcohol an organic compoundcharacterized by the presence of ahydroxyl functional group; ROH

hydroxyl group an OH functionalgroup characteristic of alcohols

H O H

(a)

R O H

(b)

R O R

(c)Figure 1Molecular models and general for-mulas of (a) water, HOH, (b) the simplest alcohol, CH3OH,methanol and (c) the simplest ether,H3COCH3, methoxymethane(dimethyl ether)

CH3

CH3

CH3

retinol(vitamin A)

CH3 CH3

OH

Alcohol ToxicityIt may be argued that all chemicalsare toxic, to widely varying degrees.Some substances, such asmethanol, are toxic in very smallamounts, while others, such asNaCl, are generally harmless inmoderate quantities. Toxicity isexpressed by an LD50 rating, foundin Material Safety Data Sheets(MSDS). It is the quantity of a sub-stance, in grams per kilogram ofbody weight, that researchers esti-mate would be a lethal dose for 50%of a particular species exposed tothat quantity of the substance. TheLD50 values for several alcohols inhuman beings are shown below.

DID YOU KNOW ??

Alcohol LD50 (g/kg body weight)

methanol 0.07

ethanol 13.7

1-propanol 1.872-propanol (rubbing alcohol) 5.8glycerol (glycerine) 31.5ethylene glycol (car antifreeze)


When an alcohol contains more than two C atoms, or more than two OH groups,we add a numbering system to identify the location of the OH group(s). This is nec-essary because different isomers of the polyalcohol have entirely different properties.The location of the OH group is indicated by a number corresponding to the C atombearing the hydroxyl group. For example, there are two isomers of propanol, C3H7OH:1-propanol is used as a solvent for lacquers and waxes, as a brake fluid, and in the man-ufacture of propanoic acid; 2-propanol (commonly called isopropanol, i-propanol, or isopropyl alcohol) is sold as rubbing alcohol and is used to manufacture oils, gums, andacetone. Both isomers of propanol are toxic to humans if taken internally.

1, 2, and 3 AlcoholsAlcohols are subclassified according to the type of carbon to which the OH group isattached. Since C atoms form four bonds, the C atom bearing the OH group can beattached to a further 1, 2, or 3 alkyl groups, the resulting alcohols classifed as primary,secondary, and tertiary alcohols, respectively (1, 2, and 3). Thus, 1-butanol is aprimary alcohol, 2-butanol is a secondary alcohol, and 2-methyl-2-propanol is atertiary alcohol. This classification is important for predicting the reactions eachalcohol will undergo, because the reactions and products are determined by the avail-ability of H atoms or alkyl groups in key positions. It is therefore useful in the selec-tion of starting materials for a multistep reaction sequence to synthesize a finalproduct.

PolyalcoholsAlcohols that contain more than one hydroxyl group are called polyalcohols; the suffixes-diol and -triol are added to the entire alkane name to indicate two and three OHgroups, respectively. The antifreeze used in car radiators is 1,2-ethanediol, commonly calledethylene glycol. It is a liquid that is soluble in water and has a slightly sweet taste; cau-tion is required when storing or disposing of car antifreeze as spills tend to attract ani-mals who enjoy the taste, but who may suffer from its toxic effects.

Another common polyalcohol is 1,2,3-propanetriol, commonly called glycerol orglycerine. Like ethylene glycol, it is also a sweet-tasting syrupy liquid, and is soluble inwater. However, unlike ethylene glycol, glycerol is nontoxic. Its abundance of OHgroups makes it a good participant in hydrogen bonding with water, a property thatmakes it a valuable ingredient in skin moisturizers, hand lotions, and lipsticks, and in foodssuch as chocolates. As you will see in Chapter 2, glycerol is a key component in themolecular structure of many fats and oils. You will also see in Chapter 2 that sugar mol-ecules such as glucose and sucrose consist of carbon chains with many attached OHgroups, in addition to other functional groups.

Section 1.5

CH3 CH2 CH2 C H

H

OH

CH3 CH2 C CH3

H

OH

CH3 C CH3

CH3

OH

CH3 CH CH3

OH

2propanol

CH3 CH2 CH2 OH

1propanol

primary alcohol an alcohol inwhich the hydroxyl functional groupis attached to a carbon which isitself attached to only one othercarbon atom

secondary alcohol an alcohol inwhich the hydroxyl functional groupis attached to a carbon which is itselfattached to two other carbon atoms

tertiary alcohol an alcohol in whichthe hydroxyl functional group isattached to a carbon which is itselfattached to three other carbon atoms

1-butanol, 2-butanol, 2-methyl-2-propanol, a 1o alcohol a 2o alcohol a 3o alcohol

Comparison of Three Isomers ofButanol (p. 84)How does the molecular structure ofan organic molecule affect its prop-erties? To find out, explore the phys-ical and chemical properties of threeisomers of butanol.

INVESTIGATION 1.5.1

polyalcohol an alcohol that con-tains more than one hydroxyl func-tional group

40 Chapter 1 NEL

The hydroxyl groups in an alcohol can also be considered an added group to a parenthydrocarbon chain; the prefix for the hydroxyl group is hydroxy-. Thus 1,2,3-propanetriolis also named 1,2,3-trihydroxypropane.

Cyclic AlcoholsMany cyclic compounds have attached OH groups, and are classified as cyclic alco-hols; many large molecules are known by their common names which often end in -ol.Menthol, for example, is an alcohol derived from the oil of the peppermint plant. Itsmolecule consists of a cyclohexane ring with attached methyl, isopropyl, and hydroxylgroups. It is a white solid with a characteristic odour, used as a flavouring and in skinlotions and throat lozenges.

A more complex cyclic alcohol is cholesterol (Figure 2), a compound that is bio-chemically significant due to its effect on the cardiovascular system. The structure ofcholesterol shows that it is a large molecule of which the polar OH group forms onlya small part, making it largely insoluble in water.

Aromatic compounds can also have attached OH groups, forming the aromaticalcohols. The simplest aromatic alcohol is a benzene ring with one attached OH group;it is named hydroxybenzene, also called phenol. Phenol is a colourless solid that is slightlysoluble in water; the effect of the polar OH group is apparent when compared withbenzene, a liquid with a lower melting point than phenol, and which is insoluble in water.Phenol is used in the industrial preparation of many plastics, drugs, dyes, and weedkillers.

When naming cyclic or aromatic alcohols, the OH (hydroxyl) groups may be consid-ered as groups attached to the parent ring. Thus, phenol is named hydroxybenzene. A ben-zene ring with two hydroxyl groups adjacent to each other is named 1,2-dihydroxybenzene.

cyclic alcohol an alcohol that contains an alicyclic ring

aromatic alcohol an alcohol thatcontains a benzene ring

CH3

CH2H2C

CHOH

H2C

CH

CH

CH

menthol

CH3H3C HO

CH CH2

CH2 CH

cholesterol

CH3

CH3

CH3

CH3

H3C CH2

OH

phenol

1. Name the following alcohol and indicate whether it is a primary, secondary, ortertiary alcohol.

First, identify the longest C chain. Since it is five Cs long, the alcohol is a pentanol.Next, look at where the hydroxyl groups are attached. An OH group is attached to the

second C atom, so the alcohol is a 2-pentanol.Look to see where any other group(s) are attached. A methyl group is attached to the

second C atom, so the alcohol is 2-methyl-2-pentanol.Since the second C atom, to which the OH is attached, is attached to three alkyl groups,

the alcohol is a tertiary alcohol.

Naming and Drawing AlcoholsSAMPLE problem

CH3CCH2CCH3

CH3

OH

CH2 CH

OHOH

1,2,3-propanetriol (glycerol)CH2

OH

CH2 CH2

OHOH

1,2-ethanediol (ethylene glycol)

Figure 2Cholesterol is only slightly soluble inwater (0

Ch1-Organic Unit 4

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