13.2.2—Terminology associated with types

Free-radical substitution replaces a hydrogen by a radical; electrophilic addition adds an electrophile across a C=C bond; nucleophilic substitution replaces a leaving group; nucleophilic addition attacks a polar carbonyl.

Curly arrows show electron-pair movement and begin at a bond or lone pair. The mechanism follows the species present, not merely the word “organic”.

In bromoethane hydrolysis, an OH⁻ lone pair attacks the carbon attached to Br while the C–Br pair leaves to Br⁻: this is nucleophilic substitution.

A curly arrow is not a reaction arrow and must not start at a positive atom. It represents a pair of electrons moving from a bond or lone pair.