General Chemistry II - Napa Valley College 240/Organic... · 4 but-5 pent-6 hex-7 hept-8 oct-9 non-...

General Chemistry | 213

Chapter Fourteen

Organic Chemistry

Organic chemistry just now is enough to drive one mad. It gives me the impression of a

primeval forest full of the most remarkable things, a monstrous and boundless thicket,

with no way of escape, into which one may well dread to enter.— Friedrich Wöhler 1835

undamentally, organic chemistry is the study of carbon compounds. These

compounds are made out of carbon, hydrogen, and oxygen with the

occasional addition of nitrogen, chlorine, bromine, phosphorus and sulfur.

Even though organic compounds only use eight of the more than one hundred

elements found on the Periodic Table, the multitude of compounds made and the

manner in which they react are dizzying.

You may know someone who has taken organic chemistry and you have

probably heard stories about large stacks of notecards filled with thousands of

reactions and the hours it takes to memorize them all. The fear of organic

chemistry grips most budding science students and it is believed that organic

chemistry is something to be survived and not enjoyed.

Much of organic chemistry is learning the language of organic chemistry. When

an instructor says to use acetone or toluene in a reaction, a structure or formula

must come to mind. It could be quite deadly to mix the wrong set of chemicals

together. To this end, we will begin our study with organic nomenclature.

Nomenclature

Nomenclature is a system for naming compounds. In organic chemistry,

nomenclature starts with a root name that is based on the number of carbons in

the longest continuous chain in the compound. The root name is a prefix, it

begins the name, and other things are added to it to clarify precisely how the

molecule is put together. Let’s start with the root prefixes.

F


Number of

Carbons

Root

Prefix

1 meth-

2 eth-

3 prop-

4 but-

5 pent-

6 hex-

7 hept-

8 oct-

9 non-

10 dec-

The dash found at the end of each name indicates that something must come

after the prefix, specifically, a suffix, that will indicate something about the

bonding occurring in the compound.

Organic chemists organize compounds by their bonding structure. In its

simplest form, compounds containing just carbon and hydrogen are broken up

into three major bonding groups.

Bonding Group General Compound Name Suffix

All single bonds Alkane -ane

One double bond Alkene -ene

One triple bond Alkyne -yne

To name a compound you combine the prefix of the root name with the suffix

that indicates the type of bond found in the compound. Therefore, compounds

like methane, propene, and butyne are all possible. These and other compounds

are shown on the next page.


Alkane Name Alkene Name Alkyne Name

Methane

Ethane

Propane

Ethene

Propene

Butene

Ethyne

Propyne

Butyne

Alkenes and Alkynes

A double or triple bond can be found anywhere within a compound. Based on

the simple rules presented thus far, it is impossible to distinguish the difference

between the following compounds,

All of these compounds have 4 carbons so generically, these are all some kind of

butene but the shape of these molecules and the placement of the double bond

changes, so they cannot all have the same name.

We can begin to distinguish between them by stating the placement of the

double bond.

1-butene 2-butene 2-butene 3-butene

C C

H2C CH3

H

H

H

C C

H3C CH3

H H

C C

H3C H

H CH3

CC

CH2H3C

H

H

H

C C

H2C CH3

H

H

H

C C

H3C CH3

H H

C C

H3C H

H CH3

CC

CH2H3C

H

H

H

H C C H

H C C C H

H

H

H C C C C

H

H H

H

H

C C

H

H

H

H

C C

H

C

H

H H

H

H

C C

H

C

H

H C

H

H

H

H

H

H C H

H

H

H C C

H

H

H

H

H

H C C

H

H

C

H

H

H

H

H


This helps, but there is no rule that says that you must start counting from the

left, but there is a rule that says that we need to keep our numbers as small as

possible. So, if we count from the right, rather than the left, we can see that,

counting from the right, 3-butene should have been named 1-butene which

makes the first and last compound on our list the same molecule.

So what about the middle two compounds both of which are named 2-butene? It

is clear that these molecules are not the same since the CH3 groups are in

different positions on the molecule. The first molecule has the CH3 groups on

the same side of the double bond and if you turn your head sideways you can

see that the general shape is “C” shaped. This form of the molecule is called

“cis” so the name of our molecule would now be cis-2-butene.

cis-2-butene

The shape of the other molecule is “trans.” This makes sense since a trans-

Atlantic flight is one that goes across the Atlantic. If we start on the first CH3

group we must go across the double bond (trans) to get to the other CH3. This

molecule is called,

trans-2-butene

You will notice that there is a dash between the various parts of this name. This

is because these are supposed to be one long name, so we connect the various

parts with dashes.

In similar fashion, we can name alkynes by adding the starting point of the triple

bond to the name.

C C

H3C CH3

H H

C C

H3C H

H CH3


1-butyne 2-butyne

Cis and trans do not apply to alkynes since their bonds are linear. Only double

bonds and rings can be cis and trans. We will discuss ring structures in a later

section.

Branching and Side Groups

A carbon chain need not be linear. It can have smaller carbon chains hanging off

of them. A carbon compound with side groups is said to be “branched.” These

side groups have the same root names as those presented earlier (meth-, eth-, etc)

but we distinguish between them and the main chain of the molecule by giving

the side groups a –yl ending. Therefore, a side group would have the following

name.

Number of

Carbons

Root

Prefix

1 methyl

2 ethyl

3 propyl

4 butyl

- Etc.

Suppose we had the following compound,

2-methylpropane

The longest chain of this compound has three carbons and it has all single bonds

so its root name is propane. But hanging off the second carbon is a methyl group

(circled in red) which must be added to the name. We must tell the reader which

side group is attached and where it is attached on the molecule so the name of

this compound is 2-methylpropane.

H C C C C

H

H H

H

H H C C C C

H

H

H

H

H

H C C

H

H

C

CH3

H

H

H

H


If there are multiple carbon side groups on a compound we must tell the reader

where each of them are located and how many there are. In addition, if they are

not all the same, then the side groups are put alphabetically into the name of the

compound. When multiple copies of the same side group show up in a

compound we tell the reader how many are present by using a common prefix

used in non-metal/non-metal nomenclature,

Number of

Side GroupsPrefix

2 di-

3 tri-

4 tetra-

5 penta-

6 hexa-

It may seem counterintuitive but we must state where every copy of a side group

is found and how many are found on a compound. For example, consider the

following,

The root name for this compound is pentane but it also has three methyl groups.

They are found on the number 2 and number 4 carbons, but since we must name

where EVERY methyl group is found AND the total number present, the name

of this compound is,

2,2,4-trimethylpentane

So we see that there is a methyl group on the number two carbon, another

methyl group on the number two carbon, and one methyl group on the number

four carbon. That makes three methyl groups so we say that this compound is a

trimethyl compound, in this case, 2,2,4-trimethylpentane.

If more than one kind of side group is present then they are placed into the name

alphabetically. Consider the following compound,

H C C

H

H

C

CH3

CH3

C

H

H

C

CH3

H

H

H

H1 2 3 4 5


This compound is six carbons long and has all single bonds, therefore its root

name would be hexane. On the number 2 carbon there are two methyl groups

and on the number 4 carbon there is a two carbon chain side group called an

ethyl group. Alphabetically, ethyl comes before methyl, so the name of this

compound would be,

4-ethyl-2,2-dimethylhexane

Halogen Side Groups

Carbon chains are not the only possible side group on a compound. Halogens

are often found as side groups of organic compounds also. To name a halogen as

a side group, the “-ine” ending of the halogen is removed and replaced with an

“o.”

Halogen NameSide Group

Name

F Fluorine fluoro

Cl Chlorine chloro

Br Bromine bromo

I Iodine iodo

As before, if we have multiple versions of the same halogen on a compound then

we number them and add di-, tri-, tetra-, etc., as appropriate. We also write them

alphabetically along with all of the other side groups. Adding chlorine and

bromine to our previous compound we would have,

5-bromo-1,3-dichloro-4-ethyl-2,2-dimethylhexane

H C C

H

H

C

CH3

CH3

C

H

H

C

CH2

H

H

H

C1 2 3 4 5

H

H

H

CH3

6

H C C

Cl

H

C

CH3

CH3

C

Cl

H

C

CH2

H

H

Br

C1 2 3 4 5

H

H

H

CH3

6


Multiple Double Bonds and Side Groups

When a compound has more than one double bond we must indicate where each

double bond starts and state whether the double bond is cis, trans, or neither cis

nor trans. For example,

The first double bond is neither cis nor trans but the second double bond is cis.

When cis and trans are used, they always start the name. When multiple double

bonds are present, you must use di-, tri, and tetra- to indicate the number. In this

case, since this compound has two double bonds, it is a diene, specifically, 1,3-

pentadiene. But, one of the bonds is cis and this must be added to the name.

You do not need to indicate which of the bonds is cis (do not write 3-cis). Any

knowledgeable reader will understand that the cis only applies to the double

bond starting on carbon number three. Therefore the full name of this

compound is,

cis-1,3-pentadiene

Ring Structures

Alkanes are not limited to linear chains of carbon compounds, they can also be

rings. When an alkane is in a ring, the prefix “cyclo” is added to the name. For

example, consider the names of the following structures,

It might seem odd to write some of these structures this way, particularly

cyclobutane which is obviously a square but has been drawn here like a

cyclopropane cyclobutane cyclopentane cyclohexane



Above the ring Below the Ring



diamond. The reason for this is that, when the hydrogen’s are added to the

compound, we attach them using vertical straight lines;

This has the added advantage of helping to indicate the shape of the molecule.

The same information can be conveyed by using dashed and solid triangular

bonds. Dashed triangular bonds are always pointing away from you and solid

triangular bonds are always pointing towards you. So, in similar fashion, we

could write,

Sometimes using triangular bonds is

the most convenient way to indicate

the shape of a molecule. For example,

in cholesterol, some of the bonds are

above the ring, others are below the

ring, and others are not on a ring but

are still pointing away from you. It is

inconvenient to attempt to draw this

large molecule in such a way that will

make these bonds easily shown. Using

triangular bonds accomplishes this

task.

H

H H

H

H H

H

H

Cholestrerol


Cis and Trans in Rings

If drawn improperly, it is impossible to know the spatial relationship between

side groups attached to rings.

It is best to draw the bonds straight up and down or use wedges and dashed

lines to indicate up and down on a ring. The reason this is important is that

rings, like alkenes, can be cis and trans. For example, consider the following

molecules,

When both chlorines are on the bottom (or top) of the ring, they are cis to each

other and when one is on top and the other is on the bottom then they are trans

to each other. The bonds in the ring behave like a double bond. They keep the

atoms rigidly held into position which allows the molecule to be either cis or

trans.

Even so, when more groups are added to a ring or across a double bond it can

get difficult to determine whether a molecule is cis or trans. For example,

Br

I

H

Cl

I

Br

H

Cl

C C

I

Br

Cl

H

C C

Br

I

Cl

H

bromoiodo-2-chlorocyclopropane bromoiodo-2-chloroethene


We can rightfully ask, which of the compounds has the name listed below it?

The answer is that both molecules have this name but in organic chemistry that is

impossible. Two molecules with different structures cannot have the same name

so there must be a way to tell the difference between them. Unfortunately, cis

and trans does not help us because it doesn’t tell us which atoms we are choosing

to be cis and trans. We must use another kind of nomenclature to describe the

differences between these molecules. We will use E, Z nomenclature.

E, Z Nomenclature

You use E and Z when cis and trans fails to properly identify similar groups.

The method relies on the Cahn-Ingold-Prelog ranking system to determine

whether a compound is cis-like (Z) or trans-like (E).

Cahn-Ingold-Prelog Ranking System

To rank the groups using EZ nomenclature the Cahn-Ingold-Prelog ranking

system is used. This system ranks the attachments one atom at a time until a

difference is found. The group that is larger FIRST, wins! For example, consider

the two side groups;

C C C

H

H

F

H

H

H

HMain Chain C C C

H

H

H

H

H

H

IMain Chain

1 2 3 1 2 3

Higher Rank Lower Rank

Starting at the main chain you go to carbon number one of the side chain. Doing

so you will find that both side groups have a CH2 attached to a carbon. Thus far,

both sides groups are equal. Moving on to carbon number two the side group on

the left has a hydrogen, a carbon and a fluorine attached to it while the one on

the right has two hydrogens and a carbon. Since fluorine is larger than a

hydrogen, the left side chain is ranked higher than the one on the right even

though the one on the right is bigger since it has iodine on it. BUT, since you got

to the fluorine (on carbon #2) before you got to the iodine (which was on carbon

#3), the left side group wins. So rank has nothing to do with overall size; it has to

do with the size of the group that you come to first.


Using this system we can resolve our problem with the nomenclature of the

molecules shown above,

If we draw an imaginary line down the middle of the bond connecting the two

carbons of interest we can rank the constituents attached to each carbon atom.

Chlorine is bigger than hydrogen and iodine is bigger than bromine. By circling

the large of the two constituents we can see that the first molecule in each group

looks “trans-like” and the second molecule looks “cis-like.” We label these E and

Z respectively and add the designation to the name.

You will notice that the E and Z designation resolves the problem of identifying

the spatial orientation of the atoms on these molecules. Unfortunately, our

problem is not completely resolved. The cyclopropane molecules shown above

are not uniquely identified by using the E, Z designation. There are two possible

H Br

ICl

H I

BrCl

E Z

C C

Cl

H

Br

I

C C

Cl

H

I

Br

E Z

bromoiodo-2-chlorocyclpropane bromoiodo-2-chloroethene

trans-like cis-like trans-like cis-like

H Br

ICl

H I

BrCl

C C

Cl

H

Br

I

C C

Cl

H

I

Br

E-bromoiodo-2-chlorocyclpropane

E-bromoiodo-2-chloroethene

Z-bromoiodo-2-chlorocyclpropane

Z-bromoiodo-2-chloroethene


configurations for both E and Z bromoiodo-2-cyclopropane. These are shown

below.

Based on the information presented thus far, both pairs of molecules would

share the same name but are actually different molecules. You will notice that

the left hand molecule and the right hand molecule in each pair are related to

each other by being non-superimposable mirror images of one another. To

provide each molecule with a unique name we must find a way of indicating to

the reader which molecule is which. We do this by using a new naming

convention called an R, S configuration.

Optical Activity

Many molecules are related to each other by being mirror images of one another.

When molecules are related in this way they are said to show “handedness”, that

is, they are related to each other like your right hand is related to your left. To

discover which molecule is left handed and which one is right handed we use the

Cahn-Ingold-Prelog method of ranking side groups to decide. Molecules that

show handedness all share one thing in common, they all have at least one

carbon with four different things attached to them.

These molecules are mirror images of each other, but they are not the

same. You cannot convert one into the other without breaking a bond.

H Br

ICl

H I

BrClE-bromoiodo-2-chlorocyclpropane

Z-bromoiodo-2-chlorocyclpropane

HI

Br Cl

HBr

I Cl


Molecules that are non-superimposable mirror images of one another are known

as enantiomers. The carbon to which the four groups are attached is known as

the “chiral” carbon and molecules that have handedness are said to be chiral or

have chirality.

Chiral molecules have another unique property; they cause light to rotate as it

passes through their solution. As a consequence, another way of saying that a

molecule is chiral is to say that the molecule shows optical activity.

The only way to tell how much light rotates as it travels through a solution is by

direct observation. A polarimeter is used for this purpose. A light source sends

light through a polarizing filter which causes the light to travel only one

direction. As this light passes through a 1 decimeter long tube of solution, the

light begins to twist. At the other end there is another polarizing filter that is

moved until the maximum amount of light is observed as it passes through the

solution. The difference in the angle between the first filter and the second filter

is the specific rotation of the organic compound. Many things effect the amount

of rotation. The concentration of the solution, temperature, length of the tube,

and even the wavelength of the light all play a role in determining the amount of

observed rotation. As a consequence, an equation is used to normalize all of

these factors and determine the specific rotation of the molecule,


ఒ[ߙ] =

ݏ ݒݎ ݐݎ ݐ

ℎݐ ℎݐ ݐ ݏݎ × ܮ/

Where T is the temperature (usually, 20°C) and λ is usually the 589 nm line of the

sodium spectrum which is also known as the “D” line. The sign of the rotation is

always given as either positive (+) or negative (-). So, if the observed angle of a

0.2 g/mL solution in a 1 decimeter tube is +1.3° at 20°C, then the specific rotation

would be,

[ߙ]ଶ =

+1.3°

1 × 0.2 ܮ/= +6.5°

Unfortunately, the actual rotation of a molecule, or even the direction of rotation

cannot be easily predicted based solely on the molecules structure, so a

convention called R,S configurations are used to determine whether a molecule is

right or left handed. This convention does not predict optical rotation and there

is no direct connection between an R, S configuration and the actual rotation of a

molecule. An R, S configuration only helps us to draw optically active

compounds and not predict how they rotate light.

R, S Configurations

The molecule, 2-butanol, has two versions, a right handed and a left handed

version. These two are optical isomers of each other and are related by being

mirror images of one another.

To distinguish between them we will use the Cahn-Ingold-Prelog ranking system

to rank the four groups attached to the central carbon atom. In this case, the

oxygen, with a mass of 16, has the highest rank (1). The next highest is the –C2H5

group (2) and then the –CH3 (3). Finally, hydrogen has the lowest rank (4) of the

four groups attached to the central carbon.


The system works best if the group of lowest rank is pointing away. In this case,

hydrogen is the lowest ranking group and it is pointing away as indicated by the

dashed line. Starting at the OH group (and ignoring the attachment of lowest

rank, the hydrogen (4)) we move clockwise until we get to the C2H5 group and

then continue clockwise to the CH3. This clockwise rotation indicates that this

molecule is right handed and is labeled R which stands for recto, the Latin word

meaning “right.” The optical isomer is S-2-butanol. The “S” stands for sinister,

the Latin word for “left.”

If the attachment of lowest priority is not pointing away then the actual rotation

will be the opposite of how it appears. For example, if we draw 2-butanol so that

the hydrogen is pointing towards us, by following the ranking of the

attachments, the molecule appears to S. But, we are looking at the molecule

wrong. The eye in the picture below is looking at the molecule from the right

direction, where the hydrogen is away. From that perspective, the red arrow is

moving clockwise or R. So although the molecule looks S to us, it is actually R,

so this molecule is R-2-butanol.


We can now resolve the problem that we had earlier with the cyclopropane

molecule.

Earlier, we called these molecules E-bromoiodo-2-chlorocyclopropane but found

that we could draw two versions of this molecule with the same name. One of

these molecules is shown above but drawn twice to show the rotation around the

two different chiral atoms in the molecule. On the left, the carbon with the blue

dot has four different groups of atoms attached to it. In order of their rank, this

chiral carbon is attached to,

1: Chlorine

2: A carbon with iodine and bromine

3: A carbon with two hydrogens

4: A hydrogen atom

The hydrogen has the lowest rank. It is on the top of the molecule and by

convention, this means that it is pointing towards us. Therefore, the rotation that

we see is opposite to the actual rotation so, although the rotation appears to be S,

it is actually R. This carbon atom is R.

In order of rank, the chiral carbon on the right molecule is attached to,

1: Iodine

2: Bromine

3: A carbon with hydrogen and chlorine

4: A carbon with two hydrogens

In this case the carbon with two hydrogens has the lowest rank and because of

the orientation of the molecule, it is pointing away from us. Therefore, the

rotation that we see is correct. The rotation is clockwise. This carbon atom is R.

Therefore, this molecule is R, R-bromoiodo-2-chlorocyclopropane. The mirror

image of this molecule would be S, S-bromoiodo-2-chlorocyclopropane. By


using R, S nomenclature rather than E, Z, the problem of their nomenclature has

been resolved.

Labeling Carbon Atoms

Sometimes it is useful to discuss molecular structures by referring to a carbon

atom by the number of other carbons attached to it. A carbon atom can have as

many as four other carbon atoms attached to it or as few as none. Each of these

conditions is given a special name, they are,

These designations sometimes show up in the names of compounds. For

example, 2-butanol is sometimes known as sec-butanol since the OH group is on

a secondary carbon. Also, it is very common to refer to 2-chloro-2-

methylpropane as t-butyl chloride, since the chlorine is on the tertiary carbon

and there are four carbons in the structure.

A molecule usually has several different kinds of carbons in its structure. For

example, the molecule below has five 1° carbons, one 2° carbon, one 3° carbon

and one 4° carbon.


Functional Groups

Hydrocarbons are not particularly reactive compounds. Since carbon and

hydrogen have very similar electronegativities (2.5 and 2.1 respectively) the

bonds between them are almost entirely covalent. This renders these molecules

essentially inert. If a highly electronegative atom like oxygen, nitrogen, or a

halogen is bonded to a hydrocarbon, these atoms polarize the molecule and this

gives the molecule a site where reactions can take place. With the addition of an

electronegative atom, hydrocarbons become reactive and can do interesting

chemistry. The kinds of chemistry that can be done depend on the nature of

these additional electronegative atoms. These atoms convert an otherwise inert

hydrocarbon into a functioning molecule capable of all kinds of chemistry. They

are, therefore, called functional groups.

Name Functional Group Name Functional Group

Alkyl Halide Acid Halide

Alcohol Acid

Amine Amide

Ether Ester

Aldehyde Ketone

Aromatic (Arene)

Alkyl Halides

As stated previously, hydrocarbons, that is, alkanes, are essentially inert. To

make them reactive an electronegative atom must be added to the compound.

While it is possible to add oxygen to a hydrocarbon, doing so is not really an

organic reaction, it is a combustion. Burning a hydrocarbon is not very useful

procedure toward organic synthesis.


Hydrocarbons are so unreactive that very few reactions are known to occur with

them. The most important of these reactions is called Free Radical Halogenation,

a reaction that converts a hydrocarbon into an alkyl halide.

CH4 + Cl2

.. ௧ሱ⎯⎯⎯⎯⎯ሮ CH3Cl + HCl

The product of Free Radical Halogenation is an alkyl halide (CH3Cl) and the

hydrohalide (HCl). Free Radical Halogenation is not restricted to chlorine;

bromine is often used and is usually preferred. The reactivity of the halogens

follows their reactivity on the Periodic Table. On a relative scale the reactivity’s

are,

Fluorine (108) > Chlorine (1) > Bromine (7×10−11) > iodine (2×10−22)

Fluorine is the most reactive, but because it is so reactive the products are

difficult to control so it is rarely used. Chlorine reactions rates are relatively fast

but not so fast that they cannot be controlled so chlorination is very common.

The bromine reaction is slow and takes high levels of UV light to cause the

reaction to go, but the reaction usually gives just one, or a few very selective

products to it is commonly used. The reaction with iodine is so slow as to be

essentially non-existent so it is not used for Free Radical Halogenation.

It is important to note that Free Radical Halogenation does not occur just

anywhere on a molecule. The halogens prefer to replace the hydrogen’s found

on the most substituted carbons. That’s just a fancy way of saying that

halogenation will occur preferentially on a tertiary carbon if one is present, or in

the absence of a tertiary carbon, halogenation will occur on a secondary carbon.

Actually, this reaction can be quite selective. Consider the following table,

Reactivity of Halogens on Various Carbons

1° 2° 3°

Chlorine 1 3.5 5

Bromine 1 97 ∞ (infinite)

This table shows us that a tertiary carbon is five times more reactive than a

primary carbon while being chlorinated, and infinitely more reactive when

brominated. If a tertiary molecule is brominated, the bromine will end up on the

tertiary carbon and nowhere else. Overall, we can see that a halogen will end up

on the most substituted carbon during Free Radical Halogenation.


The Free Radical Halogenation of an alkane is the first reaction learned by most

students in organic chemistry. The reason, of course, is because it takes a

relatively inert alkane hydrocarbon and makes it reactive by adding a halogen.

The halogen is electronegative which means that it pulls electrons toward itself

which gives the halogen a partial negative charge and makes the carbon to which

it is attached, slightly positively charged. These charges provide a site for further

reactions to occur. Thus, the relatively inert hydrocarbon is now ready to be

turned into other more interesting compounds, like alcohols.

Alcohols

Alcohols are organic compounds with –OH groups. Very often they are made

from alkyl halides. The reaction is simple enough,

Alcohols are named by adding “ol” to the root name of the longest chain. Any

molecule with an “ol” on the end is an alcohol. Cholesterol, propylene glycol

(anti-freeze), estradiol (a hormone), and nonoxynol-9 (spermicide) are all

alcohols.

When necessary, we must name where the alcohol is found along the chain.

Some common alcohols and their names are given below,


A couple of these alcohols are worthy of discussion. One of the names for

propanol is n-propanol. The “n” stands for “normal” propanol and this is

always understood as meaning propanol with the OH on the end carbon. We

would also write n-butanol and n-pentanol if these alcohols had their OH on

their end carbons.

The other alcohol that should be discussed is 2-propanol which is more

commonly known as isopropyl alcohol or rubbing alcohol. The term “isopropyl”

is common in organic chemistry so it is important that it be understood.

You will notice that the term “isopropyl” as well as “t-butyl” have the familiar

“yl” ending that indicates that it is a carbon side group, in this case, it is a side

group to an alcohol OH group. All “iso” groups can be written as

(CH3)2CH(CH2)n- where n can be any number between 0 and 3. The term “iso”

means “the same” so isobutyl means that this compound has the same number of

carbons as butane, but a different structure.


(CH3)2CH- (CH3)2CHCH2- (CH3)2CH(CH2)2-

Alcohols that are smaller than about 6 carbons are soluble in water. If the alcohol

is any larger than about six carbons, the alcohol becomes insoluble. Even though

an alcohol has an –OH group, it is not a base. Alcohols behave like acids, that is,

they give off an H+ ion. This is because the carbon-oxygen bond tends to be very

strong. The resulting structure behaves like water, where the oxygen gives off an

H+ ion.

Most of the reactions done with alcohols can be explained by remembering that

alcohols behave as acids.

Aldehydes and Ketones

Aldehydes and ketones are two of a large class of compounds called carbonyls.

Carbonyl compounds include aldehydes, ketones, acids, amides, acid halides

and esters. What all carbonyls share in common is the functional group, C=O.

What makes aldehydes and ketones different from other carbonyls is that these

compounds only have a C=O and no other electron withdrawing groups.

The only difference between an aldehyde and a ketone is where the C=O is

found. If the C=O is found on a primary carbon, then the molecule is an

aldehyde, and if it is found on a secondary compound then the molecule is a

ketone. In terms of nomenclature, an aldehyde always ends in –al, and a ketone

ends with an –one. Common ketones are acetone (used in fingernail polish

remover) and testosterone (a male sex hormone). Most aldehydes are known by


their common names. Formaldehyde is use in embalming and benzaldehyde is

the active ingredient in almond extract. Glucose is an aldehyde even though it is

not named like an aldehyde and fructose is a ketone even though there is no

indication of the presence of a ketone in its name.

Aldehydes and ketones are usually made by oxidizing an alcohol though many

other methods could be used.


Carboxylic Acids

Carboxylic acids have the functional group, COOH. They are named by adding

-oic acid to the root name of the molecule. Some carboxylic acids are shown

below along with their common names.

Carboxylic acids are generally soluble in water but when the carbon chain

exceeds about six carbons (hexanoic acid/caproic acid) the compounds become

insoluble. Very large acids like stearic acid are insoluble and they will float on

the surface of water. Nearly all oils are very large acid molecules and when they

get about twelve carbons long they are called “fatty” acids. Both lauric acid and

stearic acid are fatty acids.

All carboxylic acids are weak acids. They only partially dissociate in water.

Vinegar (acetic acid) is the most common carboxylic acid, and it smells the best.

Butanoic acid smells like rancid butter and hexanoic acid is the source of order

among goats. The Latin name for goat is “caprinus” from which caproic acid

derives its name.


Esters

Many esters smell very good. The smell of a banana, wintergreen, a crisp green

apple, and pineapple are all due to the presence of esters. As a consequence,

esters were once used in perfumes. Unfortunately, the chemical link that makes

an ester is also easily broken and so you could leave home smelling like cherries

(geranyal butyrate) but return home smelling like rancid butter (butyric acid).

As a consequence, esters are no longer used in perfumes.

Since esters are easily broken, pharmaceutical companies use the property to

their advantage. Acids often cause indigestion while esters do not. Products like

Ester-C effectively change the acidic property of vitamin c (ascorbic acid) but

make the vitamin fully available since the ester bond will be broken and the

vitamin made available in the gut. Aspirin is also an ester whose active

ingredient is salicylic acid but whose ester is more easily tolerated.

Esters are made by linking an acid with an alcohol. The link occurs through the

oxygen on the alcohol rather than the acid. The water that is produced is made

from an H+ coming from the alcohol and the OH- from the acid. This means that

the alcohol is acting like an acid (an important point that was made earlier) and

the acid is acting like a base. The general reaction is shown below,

Ester Nomenclature

The name of an ester begins with the alcohol and ends with the name of the acid.

They alcohol takes the root name of the alcohol and adds a –yl and the acid

removes the –ic acid ending and adds an –ate. In our example, the alcohol is

ethanol and the acid is ethanoic acid so the name of the ester is,

ethanol + yl ethanoic acid + ate

ethyl ethanoate

In the example above, ethanol reacts with ethanoic acid. The resulting

compound is ethyl ethanoate. Some representative esters are shown below.


Ester Name Formula Odor or occurrence

Allyl hexanoate pineapple

Benzyl acetate pear, strawberry, jasmine

Ethyl pentanoate apple

Butyl butyrate pineapple

Ethyl acetatenail polish remover, model

airplane glue

Ethyl butyrate banana, pineapple, strawberry

Ethyl hexanoate pineapple, waxy-green banana

Methyl salicylate (oil of

wintergreen)Modern root beer, wintergreen

Amyl acetate (pentyl

acetate)apple, banana

Amines

Esters smell very nice. Amines on the other hand do not. Consider yourself

fortunate if the amine only smells as bad as ammonia. Most amines have a very

offensive smell and their names often suggest the foul nature of their odor.


Names like putrescine and cadaverine suggest the odor of rotten and dying flesh

and the strong odor of fish is also associated with amines.

Amines are soluble in water since they can hydrogen bond with water. Like

most other organic compounds, only the smaller amines are soluble because as

the chain length grows, dispersion forces take over making the compounds

insoluble.

Amine Nomenclature

Amines are distinguished by the presence of an –NH2 on an alkane. There are

two ways in which this group is used in the name of a compound, either as a side

group called an “amino” group, or as the main functional group when it is called

an “amine.”

When an –NH2 is the main functional group “amine” is added as a suffix to the

root name of the compound. Unfortunately, there is great variation in the

nomenclature of amines and sometimes the carbon chain is expressed like a side

group and given a –yl ending, and depending on the situation, the –NH2 can be

described as a side group and it takes on the typical “o” of a side group (chloro,

oxo, amino).

CH3-CH2-CH2-NH2

propane + amine = propanamine

propylamine

aminopropane

All three of these names can be found as the name of this compound. Many

compounds that do not end in “amine” are amines but their name will indicate

the presence of the amine by ending in “in” or “ine.” There are many such

compounds that we use in daily life, most of them act as drugs.

Penicillin

Amoxicillin

Epinephrine

Ephedrine

Morphine

Dopamine

Serotonin

Acetaminophen


Primary Amines

Amines can be divided into four groups, primary, secondary, tertiary, and

quaternary amines. These designations indicate the number of carbon chains

attached to the amine group. Propanamine is a primary amine since it has only

one carbon chain attached to it. Other primary amines are given below.

Secondary Amines

Secondary amines are compounds with two carbon chains attached to the amine

group. Very often, the longest carbon chain is chosen as the root name and the

shorter carbon chain is selected as a side group. Technically, it is possible to

have the shorter side group found anywhere on the compound, but since it is

attached to the nitrogen (as opposed to the longer main chain) then an “N” is

used to describe this position. For example, suppose that we have the following

compound;

CH3-NH-CH2-CH2-CH3

The longest chain has three carbons so the root name of this compound,

including the amine group, is propanamine. Since this compound also has a

methyl group attached to the nitrogen, the full name of this compound would be,

N-methylpropanamine.

It is also possible to name this compound by listing the carbon chains as side

groups. In this case, this compound would be called methylpropylamine or N-

methylpropylamine. In similar fashion, if both side chains are the same, then the

name of the following compound would be diethylamine,

CH3-CH2-NH-CH2-CH3

diethylamine

A number of secondary amines are given below,


Tertiary Amines

Tertiary amines have had all of their hydrogen’s replaced with carbon chains.

Even without a nitrogen-hydrogen bond, these molecules can still bond through

their lone pair electrons so these compounds are usually soluble in water.

General Chemistry II - Napa Valley College 240/Organic... · 4 but-5 pent-6 hex-7 hept-8 oct-9 non-...

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