Functional groups

Functional groups determine the properties of the entire molecule. It is a group of atoms which gives a characteristic set of properties to a molecule containing that group.

 

Alkane

Insoluble with water (no polarity)

Will undergo substitution reaction with halogens, forming a haloalkane, hydrogen halide

Slowly, in the presence of UV light

General formula: CnH2n+2

 

Primary alcohol

RCH2OH

All alcohols contain hydroxyl groups

Can be oxidised to form aldehydes, then carboxylic acids

As it has OH group, it can react with sodium to produce hydrogen

General formula: CnH2n+2O

Nomenclature: -anol

Boiling point: H-bonds; as molecule gets larger, dispersion does too

Physical properties: small alcohols infinitely soluble in water

Chemical properties: similar to water

Can react with water to form acid/base

e.g. ROH + H2O –> RO + H3O+

 

Secondary alcohol

R2CHOH

Can be oxidised to form ketones

Reacts with sodium to form H2

 

Tertiary alcohol

R3COH

Cannot be oxidised.

Reacts with sodium to form H2

 

Aldehyde

RCHO

Have a carbonyl group on the end of a chain

Can be reduced to form primary alcohols, and oxidised to carboxylic acids

General formula: CnH2n+2CHO

Nomenclature: -anal

Production: incomplete or controlled oxidation of primary alcohol

Boiling point: Dipole-dipole

Physical properties: small molecules soluble in water due to electrons on carbonyl group

 

Ketone

RCOR

A pair of alkyl groups attached to a carbonyl group

Can be reduced to form secondary alcohol, cannot be oxidised

General formula: CnH2nO

Nomenclature: -anone

Production: incomplete or controlled oxidation of primary alcohol

Boiling point: Dipole-dipole

Physical properties: small molecules soluble in water due to electrons on carbonyl group

 

Carboxylic acid

RCOOH

An alkyl attached to a carbonyl-hydroxyl group.

Weak Bronsted-Lowry acid.

Reacts with sodium to form H2

General formula: CnH2n+1COOH

Nomenclature: -anoic acid

Production: complete oxidation of primary alcohol

Boiling point: high, due to H-bond

Physical properties: small molecules soluble in water

Chemical properties: Readily neutralised by alkalis

RCOOH + OH –> RCOO + H2O

But if in aqueous solution,

RCOO + H2O <–> RCOOH + OH

So pH is above 7 if ‘neutralised’

 

Ester

RCOOR

Two alkyls attached to a carbonyl and linking oxygen

Smells fruity

Nomenclature: First: alcohol becomes “yl” Second: ‘oic’ becomes ‘oate’

Production: esterification: mixture of alcohol and carboxylic acid. Very slow rate, so catalyst of H2SO4 and high temps are used. Water is formed from the OH in the acid and a H from the alcohol.

Primary amine

RNH2

An amine group at the end of an alkyl chain.

Able to be protonated to form a ammonium ion group

Small – smells pungent. Large – smells fishy

Ammonia reacts with a haloalkane to form protonated amine + halide ion, then amine + hydrogen halide

 

Amino acid (alpha)

Alpha amino acids have R, COOH and NH2 on the same carbon atom (the alpha carbon atom)

R-CH(NH2)COOH

May form zwitterions

Alkene

Double bond

General formula: CnH2n

Reactions:

Addition of halogens across double bond

Addition of hydrogen halides across double bond

Addition of water to form alcohol

 

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