Functional groups

A long carbon chain is chemically dull — C–C and C–H bonds are strong, non-polar and unreactive. Nearly everything interesting happens at a functional group: a small arrangement of atoms with its own reliable behaviour.

Recognising a group predicts common reaction patterns. The rest of the molecule, steric hindrance and reaction conditions can change its reactivity and products. That is the single biggest labour-saving idea in the subject.

The groups also have a strict seniority order, which decides what a molecule is named after when it contains several:

carboxylic acid > ester > amide > nitrile > aldehyde > ketone > alcohol > amine > alkene/alkyne > halide

The most senior group present becomes the name's suffix; everything below it becomes a prefix.