Organic Chemistry and Functional Groups
Core concepts
Organic chemistry is organised by functional group, which determines reactivity. Candidates must recognise alkanes (single bonds, substitution), alkenes and alkynes (multiple bonds, addition), alcohols (hydroxyl), aldehydes and ketones (carbonyl), carboxylic acids, esters, amines, and halogenoalkanes.
Nomenclature follows IUPAC rules: longest chain, lowest locants, suffix for the principal group. Isomerism includes structural (chain, position, functional group) and stereoisomerism (geometric cis/trans and optical).
Reaction types must be matched to functional groups: addition for alkenes, substitution for alkanes and halogenoalkanes, oxidation of alcohols to aldehydes/ketones and then acids, esterification between alcohol and carboxylic acid, and polymerisation.
Traps to watch
- Confusing aldehydes and ketones - only aldehydes are oxidised readily (e.g. by Tollens' reagent).
- Forgetting that primary alcohols oxidise to aldehydes then acids, while secondary alcohols give ketones.
- Assigning cis/trans to molecules without restricted rotation.
- Miscounting the longest chain when branches are present.
- Assuming all isomers have identical physical properties.
Worked example
Name CH₃CH₂CH₂OH: longest chain three carbons (propan-), hydroxyl suffix (-ol) at position 1, so propan-1-ol. Rule of thumb: find the longest chain first, then number to give the principal functional group the lowest locant.