Isomerism

Question 1

What are isomers?

Answer 1

Molecules with the same molecular formula but a different arrangement of atoms within the molecule

Question 2

What are structural isomers?

Answer 2

They have a different structural arrangement of atoms. They can be straight chains or branched chains but will have the same molecular formula.
E.g. C4H10 - Butane and 2 - methylpropane

Question 3

What are positional isomers?

Answer 3

These have the functional group of the molecule in a different position of the carbon chain. E.g. propan-1-ol and propan-2-ol

Question 4

What are functional group isomers?

Answer 4

These have a different arrangement of the same molecular formula so that the molecule has a different functional group. E,g. C6H12 - Hexene and Cyclohexane

Question 5

What are stereoisomers?

Answer 5

These have a different spatial arrangement. A type of stereoisomerism is E-Z isomerism where limited rotation around a double carbon bond means that groups can either be ‘together’ or ‘apart’. The E isomer (german for entgegen meaning apart/opposite) has these groups apart. The Z isomer (german for zusammen meaning together) has these groups on the same side of the double carbon bond. E.g. (E) 1,2 - dichloroethene and (Z) 1,2 - dichloroethene

Question 6

What are the Cahn-Ingold-Prelog (CIP) priority rules?

Answer 6

There is a priority of different groups in molecules that can display E-Z isomerism. The atom or group on each side of the double bond with the higher Ar or Mr is given the higher priority. These groups are used to determine if it is the E or Z isomer.