Reference—AS organic functional groups

A functional group is the atom or bond arrangement that gives an organic molecule its characteristic reactions. At AS level, recognise alkenes, halogenoalkanes, alcohols, aldehydes, ketones, carboxylic acids, esters and amines from their structures.

Identify the group before choosing a reagent or mechanism. For example, C=C suggests addition chemistry, C–X suggests substitution or elimination, and C=O distinguishes carbonyl compounds from hydrocarbons.

CH₃CH₂OH is an alcohol because it contains –OH; CH₃CHO is an aldehyde because the carbonyl carbon is bonded to H. The names follow the structure, not the other way round.

A functional group is not just a substring in a name. Check connectivity and distinguish an aldehyde, ketone, acid and ester carbonyl.