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

2. 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

3. 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

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

5. 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

6. 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

7. 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

8. 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

9. 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)

10. 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

11. 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

12. 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

13. 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

14. 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:-

15. (continued) HCOOCHCH 3 CH 3 2-methylethyl methanoate