Organic Chemistry
Organic Chemistry
This domain tests homologous series, functional groups, IUPAC naming, isomerism, reaction types and simple tests. The exam expects you to identify a functional group, name a compound and predict a reaction product or test result.
Core rules
- Alkanes: single bonds, substitution with halogens in UV light. Alkenes: C=C, addition reactions and decolourisation of bromine water.
- Alcohols: hydroxyl group; primary alcohols oxidise to aldehydes then carboxylic acids, secondary to ketones, tertiary resist oxidation. Acidified potassium dichromate(VI) turns from orange to green.
- Aldehydes reduce Fehling's solution to a red precipitate and Tollens' reagent to a silver mirror; ketones do not.
- Carboxylic acids plus alcohols form esters with a concentrated acid catalyst; esters have characteristic sweet smells.
- Halogenoalkanes undergo substitution with aqueous alkali and elimination with alcoholic alkali.
- Isomers have the same molecular formula but different structures; structural isomers differ in connectivity.
Worked example
Propan-1-ol, CH3CH2CH2OH, is a primary alcohol. With acidified potassium dichromate(VI) and distillation, it is oxidised to propanal, CH3CH2CHO. With excess oxidant and reflux, propanal is further oxidised to propanoic acid, CH3CH2COOH. Propan-2-ol, a secondary alcohol, gives propanone instead.
Traps
Do not label a compound an alkene when the structure contains only single bonds. Distinguish distillation from reflux: distillation removes the aldehyde before further oxidation; reflux allows complete oxidation. Test results must name the reagent and the observed change, not just that it reacts.