Ch 5 - **Acetal** — Chs 25, 31 (protecting group); see *App F* - **Acetic acid** — Chs 3, 26 - **Acetylcholinesterase** — Ch 35 - **Acetyl-CoA** — Chs 28, 34 - **Activating groups** — Ch 22 - **Activation energy** — Ch 5 - **Acyl substitution** — Ch 26 - **Adamantane** — Ch 5; *App H* - **Adenine**