ISOMERISM There are two main types of isomerism Structural i.e.molecular positional functional group Stereoisomerism i.e.Geometric and Optical

Molecular This is something you are already aware of from previous work. i.e. CH 3 CH 3 CH 2 CH 2 CH 3 CH 3 CHCH 3 Butane 2-methylpropane

Positional You are also aware of most of these from alcohols and halogenoalkanes e.g. Cl CH 3 CH 2 CH 2 OH CH 3 CHCH 3 Propan-1-ol 2-chloropropane However we need to consider aromatics

Positional (aromatics) X X X X X 1,2- (ortho) 1,3- (meta) 1,4- (para)

Functional group There are three main pairs of homologues involved here, namely:- 1. Alcohols and ethers (alkoxyalkanes) 2. Alkanals and alkanones 3. Alkanoic acids and esters

Functional group Alcohols and alkoxyalkanes e.g. For the general molecular formula C 2 H 6 O it is possible to have:- CH 3 CH 2 OH and CH 3 OCH 3 Ethanol Methoxymethane

Problem Write out all possible isomers of C 4 H 10 O together with their systematic names. CH 3 CH 2 CH 2 CH 2 OH Butan-1-ol CH 3 CH 3 CHCH 2 OH 2-methylpropan-1-ol

C 4 H 10 O CH 3 CH 2 CHCH 3 OH Butan-2-ol CH 3 CH 3 CCH 3 OH 2-methylpropan-2-ol

C 4 H 10 O (continued) CH 3 CH 2 OCH 2 CH 3 Ethoxyethane (diethyl ether) CH 3 OCH 2 CH 2 CH 3 Methoxypropane (methyl propyl ether)

Alkanals and alkanones For the general molecular formula C 3 H 6 O it is possible to have:- CH 3 CH 2 CHO and CH 3 COCH 3 Propanal Propanone

Problem Write out all possible isomers of C 4 H 8 O together with their systematic names CH 3 CH 2 CH 2 CHO CH 3 CHCHO CH 3 Butanal 2-methylpropanal CH 3 CH 2 COCH 3 Butanone

Alkanoic acids and esters For the general molecular formula C 2 H 4 O 2 it is possible to have CH 3 COOH and HCOOCH 3 Ethanoic acid Methyl methanoate

Problem Write out all possible isomers of C 4 H 8 O 2 together with their systematic names CH 3 CH 2 CH 2 COOH CH 3 CHCOOH CH 3 Butanoic acid 2-methylpropanoic acid

C 4 H 8 O 2 (continued) CH 3 COOCH 2 CH 3 Ethyl ethanaoate CH 3 CH 2 COOCH 3 Methyl propanoate HCOOCH 2 CH 2 CH 3 Propyl methanoate There is one other ester which occurs:-

(continued) HCOOCHCH 3 CH 3 2-methylethyl methanoate