Reference—A Level organic functional groups

A functional group is the reactive arrangement of atoms that gives an organic molecule characteristic reactions. Identify it from connectivity, not from the molecule’s name alone.

The syllabus representations include families such as alkenes (C=C), halogenoalkanes (C–X), alcohols (C–OH), aldehydes (–CHO), ketones (>C=O), carboxylic acids (–CO₂H), esters (–CO₂–), amines and nitriles (–C≡N).

Propanal and propanone both contain C=O, but the aldehyde has a terminal –CHO group whereas the ketone has carbonyl carbon bonded to two carbon groups; that difference predicts different oxidation behaviour.

Do not classify a molecule by spotting one atom. The neighbouring bonds and position decide whether the group is, for example, an alcohol, ether, aldehyde or carboxylic acid.