Medium Practice — Set 2

Quick Recap — Electronic Effects & Intermediate Stability

• Carbocation stability: $3^\circ>2^\circ>1^\circ>$ methyl; benzyl/allyl are resonance-stabilised.
• Free radicals: $3^\circ>2^\circ>1^\circ$; carbanions: stabilised by $-I$/$-M$ (so $CCl_3^->CH_3^->3^\circ$).
• Resonance (mesomeric): $+M$ donors ($-OH$, $-NH_2$, $-OR$, $-X$ lone pairs) enrich ortho/para; $-M$ acceptors ($-NO_2$, $-CN$, $-CHO$, $-COOH$) withdraw.
• Hyperconjugation (no-bond resonance): more $\alpha$-H $\Rightarrow$ greater stability of the cation/alkene.