Chapter 23Functional groups

23.1 Introduction to functional groupsNot all substituents are carbon and hydrogen

A large amount of diversity exists between substituent components,and can contain oxygen, nitrogen, sulphur or phosphorus

These elements can make the substituent reactive, and are called functional groups

A functional group is a specific arrangement of atoms in an organic compound that helps predict how the compound will behave in a reaction

Identifying functional groups is an important skill!

As double and triple bonds are chemically reactive they are also classified as functional groups

AmideAmideCarbonylAldehyde

EsterEtherEther

CarbonylCarboxylic acid

HalogenHalocarbon

CarbonylKetone

EsterAminoAmine

HydroxyAlcohol

Functional group

General structure

Compound type

Functional group

General structure

Compound type

Organic Compounds Classified by Functional Group

What does the R stand for?

• In each general structure listed, the symbol R represents any carbon chains or rings attached to the functional group.

• When more than one R group is shown in the structural formula, the groups do not need to be the same.

• In some cases, R can be a hydrogen atom.

Halocarbons ● A halocarbon is an organic compound that contains at least one covalently

bonded fluorine, chlorine, bromine, or iodine atom.● The general formula of a halo carbon is RX, where X is a halogen substituent.● The IUPAC rules for naming halocarbons are based on the name of the

parent hydrocarbon.○ The halogen groups are named as substituents

ChloromethaneChloroethene

Are common names different? ● Yes!!● Common names of halocarbons consist of two parts.● The first part names the hydrocarbon portion of the molecule as an alkyl

group, such as methyl- or ethyl-.● The second part names the halogen with an -ide ending.

Methyl chloride Vinyl chloride Phenyl chloride

Halocarbon naming continuedOn the basis of their common names, a halocarbon in which a halogen is attached to a carbon of an aliphatic chain is called an alkyl halide.

A halocarbon in which a halogen is attached to a carbon of an arene ring is called an aryl halide.

Properties of halocarbonsThe attractions between halocarbon molecules are primarily the result of weak van der Waals interactions.

Generally, these attractions increase with the degree of halogen substitution.

Compounds that are highly halogenated with have higher boiling points

40 85.0

Dichloromethane (methylene chloride)

CH2Cl2

61119.5Trichloromethane (chloroform)CHCl3

74154.0Tetrachloromethane (carbon tetrachloride)

CCl4

–24Chloromethane (methyl chloride)CH3Cl

–161 16.0MethaneCH4

50.5

Boiling point (°C)

Molar mass (g)NameMolecular

formula

Comparing Methane and Chloromethanes

Why are they useful? Very few halocarbons are found in nature, but they can be readily prepared and used for many purposes.

For example, hydrofluorocarbons (HFCs) are used as refrigerants in automobile air-conditioning systems.

Halocarbons are also used as solvents and as ingredients of stretchable polymers

What is a substitution reaction? A reaction in which one atom or group of atoms replaces another

This is a very common type of organic reactions

Organic reactions tends to proceed slowly, as they involve the breaking of covalent bonds - as such catalysts are often needed

Substitution reactions provide a mechanism to introduce new functional groups to organic molecules

Examples

A halogen atom can replace a hydrogen atom on an alkane to produce a halocarbon.• The symbol X stands for a halogen in this

generalized equation.

R—H + X2 → R—X + HX Alkane Halogen Halocarbon Hydrogen halide

Other examples of halogenation

UV lightCH4 + Cl2 → CH3Cl + HCl

Methane Chlorine Chloromethane Hydrogen chloride

Sunlight or another source of ultraviolet radiation usually serves as a catalyst.

Alcohols, Ethers and Amines

Section 23.2

What do mouthwash, perfume, and hairspray have in common?They all contain an alcohol of some type.An alcohol is an organic compound with an —OH group.

The OH group is referred to as a hydroxy group or hydroxyl group

The electron arrangement in the -OH group gives the oxygen a bent shape

Categories of aliphatic alcohols

● Aliphatic alcohols can be categorised into structural categories

● These categories are based on the the number of carbon atoms attached to the carbon with the hydroxy group

● Sometimes only 1 carbon is attached to the -OH group, in which case the bonded carbon is a primary carbon

● If two carbons are attached it is a secondary alcohol

● If three carbons are attached it is a tertiary alcohol

How do you name an alcohol

● Both IUPAC and common names exist● In the IUPAC name you drop the e from

the end of the parent hydrocarbon name and add -ol

● When numbering carbons, the hydroxy group is given the lowest possible carbon number

● If an alcohol contains more than one hydroxy group the ending changes again

○ -diol if two alcohols○ -triol of three alcohols

Ethanol

2-propanol

Common names Common naming is very similar as with halocarbons

The first part names the hydrocarbon portion of the molecule

The second part names the hydroxy group

If the alcohol is attached to an aromatic ring, the compound is called a phenol

Alcohol propertiesAlcohols are capable of hydrogen bonding

This affects the physical properties of alcohols - they boil at higher temperatures than alkanes and halocarbons that contain a similar number of atoms

The hydroxy group makes alcohols somewhat soluble in water

Alcohols up to 4 carbons long are completely soluble in water, whereas those with more than 4 have a much lower solubility

The hydroxy group is polar - it can therefore bond to a water molecule, yet the carbon chain is non polar

What are some industrial uses of alcohol?A moistening agent in cosmetics, food, medicines

Antifreeze

Alcoholic beverages

Ethanol - produced by fermentation of sugars from yeast or bacteria

Addition reactions● The carbon to carbon single bond is hard to break● The double bond in an alkene is much easier to break● In an addition reaction a substance is added at the double or triple bond of an

alkene or alkyne● Addition reactions are an important method of introducing new functional

groups to organic molecules, and by converting alkanes to alkenes

Hydration reactionsThe addition of water to an alkene is called a hydration reaction

A hydration reaction forms an alcohol

An acid usually serves as the catalyst

Hydrogenation reactionsThe addition of hydrogen to a carbon-carbon double bond to produce an alkane is called a hydrogenation reaction

This normally needs a catalyst

Platinum or Palladium is a common catalyst

Ethers An ether is an organic compound in which oxygen is bonded to two carbon groups

The general formula is R-O-R

How do you name an ether? When using the IUPAC system, you begin with identifying the two R groups

The smaller forms part of the substituent

The ane or ene ending is replaced with - oxy

The larger is the parent hydrocarbon

And common names? In common names both of the R groups are treated as substituents

The -ane or -ene endings are replaced with -yl for both R groups

These R groups are then listed in alphabetical order

Finally the word ether is added at the end

What about if the ether is symmetrical? In the Oxygen position results in a symmetrical ether, the IUPAC name is unchanged.

In the common name the prefix -di is added before the two substituent groups

What are ethers used for, what are their properties? Ethers are commonly used an extractant, or as an anesthetic

They tend to have lower boiling points than alcohols of comparable molar mass

Ethers have higher boiling points than hydrocarbons and halocarbons

Ethers can not form hydrogen bonds with other ether molecules, but they can with water - why?

Ethers are more soluble in water than hydrocarbons and halocarbons

Ethers are less soluble in water than alcohols - ehy?

AminesIn an amine, a nitrogen is binded to a carbon group

Similar to ammonia, but carbon groups can replace one, two or three of the hydrogens

Amines can be classified by the number of hydrogens attached to the nitrogen atom

The general formula is RNH2 (primary), R2NH (secondary) or R3N (tertiary)

What kind of amine is this?

Naming aminesAmines are named the same way as alcohols

The -e ending of the parent hydrocarbon is changed to -amine

For common names you name the alkyl or -aryl group and then follow it by -amine

Do amines form hydrogen bonds? Yes, primary amines do

Nitrogen is less electronegative than oxygen, so hydrogen bonds are weaker than those in alcohols

How do the boiling points of primary arines compare to alcohols?

Are Amines soluble in water?

Carbonyl compoundsSection 23.3

Aside from an ether and an alcohol, how else could an O be incorporated into a hydrocarbon?● An oxygen can be bonded to carbon by a double bond● This is referred to as a carbonyl group● The carbonyl group forms a fundamental part of aldehydes and ketones● Aldehyde - the carbon of the carbonyl group is bonded to at least one

hydrogen● Ketone - the carbon of the carbonyl group is bonded to two other carbons

How do you name Aldehydes and KetonesUsing the IUPAC system for either class of system it is important to name the longest carbon chain that contains the carbonyl group

For an aldehyde the -e ending is is replaced with an -al

Ketones the -e is replaced to -one

Sometimes a carbonyl group of a ketone can occur at more than one position on a chain, if so position is determined by the lowest possible number

Examples

Benzaldehyde(benzaldehyde)

Ethanal(acetaldehyde)

Methanal(formaldehyde)

IUPAC name (common name)

Ball-and-stick model

Structural formulaSome Common Aldehydes Examples

Diphenylmethanone(benzophenone)

Propanone(acetone)

IUPAC name (common name)

Ball-and-stick modelStructural formula

Some Common KetonesWhat are aldehydes and ketones used for? ● Methanal (formaldehyde) is the simplest aldehyde

○ Common use is in the manufacture of synthetic resins○ Aromatic aldehydes are contained in many flavoring agents

● Propanone is the most common ketone○ Also known as acetone○ Used as a common solvent

Can they form hydrogen bonds? ● No! ● No hydrogen bonded to the oxygen, therefore no difference in

electronegativity● Therefore lower boiling points when compared to alcohols ● The carbonyl groups can however attract each other - a weak force of

attraction, making the boiling point higher than corresponding alkanes● All aldehydes or ketones are solid or liquid at room temperature

Summary so far

Hydrogen bonding97CH3CH2CH2OH1-Propanol

Polar-polar interactions56CH3COCH3Propanone

Polar-polar interactions49CH3CH2CHOPropanal

Dispersion forces –42CH3CH2CH3Propane

Primary intermolecular

interactions

Boiling Point (°C)FormulaCompound

Some Organic Compounds with Three CarbonsCarboxylic acids A carboxyl group is a carbonyl group attached to a hydroxy group - COOH

This forms a carboxylic acid

General formula RCOOH

Naming carboxylic acid In the IUPAC system, carboxylic acids are named by replacing the -e ending of the parent structure with the ending -oic acid.

Remember, the parent hydrocarbon of a carboxylic acid is the longest continuous carbon chain containing the carboxyl group.

The carboxylic acid CH3COOH is named ethanoic acid.

Properties and uses of Carboxylic acids ● Carboxylic acids are weak acids. They

ionize weakly in solution● In water they can lose a hydrogen ion and

form a carboxylate ion ● Do they form hydrogen bonds ?● Yes!● They therefore have higher boiling and

melting points than other compounds of similar molar mass

● Ethanoic acid - (vinegar) is a common use of carboxylic acids

● Fatty acids are a type of carboxylic acid

Oxidation and reduction reactions with hydrocarbons

● In organic chemistry the number of oxygen and hydrogen atoms indicates the degree of oxidation of a compound

● The less hydrogens in a carbon carbon bond the more oxidized it is● A triple bond is more oxidized than a double bond that is more oxidized than a

single bond● A dehydrogenation - the loss of a hydrogen molecule

Sometimes oxidation can occur in a series of steps...

EstersEsters are hydrocarbons with a distinctive smell

It is an organic compound in which the -OH of the carboxyl group is replaced by an -OR from an alcohol

Esters contain a carbonyl group and an ethyl link to the carbonyl group

General formula -RCOOR

Can Esters form hydrogen bonds

Esters are polar but do not form hydrogen bonds with one another

Esters do not contain hydrogen attached to oxygen or nitrogen or fluorine - why does this matter?

Only weak polar polar interactions hold ester molecules to one another

Esters have much lower boiling points than carboxylic acids

How are esters made? Esterification

The reactants are usually a carboxylic acid and an alcohol

They are heated with an acid as a catalyst PolymersSection 23.4

What is a polymerA polymer is a long chain of molecules that makes up monomers

They are formed by covalent bonding of repeating smaller molecules - these are referred to as monomers

Some polymers contain one type of monomer, some contain many

Polymerization is the reaction that combines monomers to form polymers

There are two types of polymers

Addition

Condensation

Example of addition polymerization Ethene undergoes addition polymerization to form polyethene

Parentheses on the product side indicate the repeating unit

PolyethyleneMany polymers, such as polyethylene have a number of very useful properties

Polyethylene is used to make plastic bottles, containers and toys

When polyethylene has short chains (x = 100) it is soft like paraffin wax,

When polyethylene has long chains (x = 1000) it is harder and rigid

Polypropylene Polypropylene is stiffer than polyethylene

This is used for utensils and beverage containers

It is prepared by the polymerization of propene

What is Polystyrene used for? Polystyrene in a rigid foam does not conduct heat well, so is useful for insulation of homes

Often used in cups, picnic coolers

Prepared by the polymerization of styrene

What is polyvinyl chloride (PVC) used forMany halocarbon polymers (including PVC) have many useful properties

PVC is used for clothing, in plumbing, fabrics

What is Polytetrafluoroethylene used for? PTFE is a substance highly resistant to heat and chemicals

Commonly known as Teflon

Used as a coating on nonstick cookware

Polyisoprene Polyisoprene is the polymer that constitutes natural rubber

The monomer of polyisoprene, isoprene, is harvested from tropical plants such as the rubber treePolyisoprene is used to make rubber bands, soles of athletic shoes, and many other common items.

Rubber is harvested from tropical plants. Harvesters cut the trees, and the sap, which contains isoprene, is collected.

As the rubber dries, the isoprene polymerizes and changes form.

Finally, the manufacturer processes and molds the polymer to form the desired product.

Condensation reactionsNot all polymers from from simply joining molecules together

Some instead involve the loss of a small molecule during this formation process - example - water

Polyester is a common example

Formed from repeating dicarboxylic acids and dihydroxy alcohols - these are joined by ester bond

Drawing condensation reactions● These reactions can be represented by a block diagram, in which only the

functional groups involved in the reaction are shown ● Squares and circles represent unreactive parts ● Condensation polymerization requires two functional groups on each

monomer molecule

What is this made of? ● PET is an abbreviation of the

polyester polyethylene terephthalate . PET is formed from terephthalic acid and ethylene glycol

● PET is readily recycled - water bottles can be turned into a fleece

● 12 water bottles can make one jacket

● PET is melted and forced through tiny holes in devices to make fibres - often combined with cotton

PolyamidesA polyamide is formed when you mix a carboxylic and an amine

These result in a polymer with an amino (NH2) functional group

This is a condensation reaction

What is nylon? Nylon is a type of polyamide commonly used to make strong fibres in ropes, carpeting, fishing lines and textiles

It forms from 6-aminohexanoic acid

This one compound contains both necessary functional groups

The long polymer chain if formed by combining the carboxyl group at one end to the amino group at the other end

What is Kevlar? Kevlar is a polyamide that contains an aromatic ring

Any polyamide that contains an aromatic ring is extremely tough and fire resistant

They also have the benefit of being light and flexible