A Level organic chemistry conventions and functional group reference

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.

Benzene is represented in A Level structures by a hexagonal ring with alternating bonds or a circle, depending on the required convention. When benzene is part of a molecule, the ring is not normally redrawn as a fully displayed set of C–H bonds.

Attach substituents to the ring at the correct carbon and use the ring symbol consistently in condensed, skeletal and displayed representations.

Phenol can be shown as a benzene ring bonded to –OH; methylbenzene is the same ring bonded to –CH₃. The ring itself supplies the six-carbon aromatic framework.

The circle is not a seventh atom and the alternating-bond drawing is not three isolated double bonds behaving independently; both conventions represent the delocalised ring.