A nucleophilic addition reaction differs from a nucleophilic substitution reaction in that addition:

1. Both reactions involve a nucleophile, an electron-rich species seeking a positive centre. 2. In nucleophilic addition the nucleophile adds across a multiple bond, and nothing leaves the molecule. 3. In nucleophilic substitution the nucleophile replaces a group already attached, which departs as a leaving group. 4. Removing two groups to create a multiple bond is elimination, a third reaction type entirely. 5. Explaining substitution when addition was asked for was the single most common recorded error on this question. _Source: NECTA ACSEE 2024 Chemistry 132/1, Question 1: Aliphatic Hydrocarbons_