13.2 Characteristic organic reactions

A homologous series shares a functional group and general formula, with successive members differing by CH₂. Saturated compounds contain no carbon–carbon multiple bond; unsaturated compounds do.

Homolytic fission splits a bond evenly to form radicals, while heterolytic fission gives both electrons to one atom and forms ions. In radical chemistry, initiation creates radicals, propagation consumes and regenerates them, and termination removes radicals.

UV light can split Cl₂ homolytically: Cl₂ → 2Cl·. A chlorine radical then abstracts H from methane, beginning a propagation chain.

A radical is not simply an ion, and “unsaturated” does not mean every bond is weak. Match the term to the electron movement shown.

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.