Chapter 8 Summary and Reaction Summary Table
Chapter 8 Summary & Reaction Summary Table
Carbonyls (aldehydes and ketones) are electrophilic at the carbonyl carbon and undergo nucleophilic addition with predictable outcomes. Use this page as a quick map of the core transformations.
Key Nucleophilic Additions
- Hydration → gem-diols: H₂O (acid or base catalyzed).
- Cyanohydrins: ⁻CN with slight acid.
- Acetals/hemiacetals: ROH (acid, remove water) → protecting groups.
- Imines/enamines: 1° amine → imine; 2° amine → enamine (mild acid, pH ~5).
- Hydrazones/2,4-DNP/oximes: Carbonyl + NH₂NH₂ / 2,4-DNP / NH₂OH → diagnostic derivatives.
- Hydride reduction: NaBH₄ or LiAlH₄ → alcohols.
- Grignard/organolithium: RMgBr/RLi → alcohols with new C–C bond (1°, 2°, 3° depending on carbonyl).
- Wittig: Ph₃P=CHR → alkene + Ph₃P=O.
Reaction Summary Table
| Reaction | Typical reagents | Product / note |
|---|---|---|
| Hydration | H₂O (H⁺ or OH⁻) | Geminal diol (favored for formaldehyde; reversible) |
| Cyanohydrin | NaCN/KCN, slight acid | R₂C(OH)–C≡N; reversible; handle CN safely |
| Hemiacetal/acetal | ROH, acid, remove H₂O | Protect carbonyl; hydrolyze with aqueous acid |
| Imine formation | 1° amine, pH ~5 | C=NR (Schiff base); reversible hydrolysis |
| Enamine formation | 2° amine, pH ~5 | C=C–NR₂; formed via iminium then deprotonation |
| Hydrazone/2,4-DNP/oxime | H₂NNH₂ / 2,4-DNP / NH₂OH | Stable derivatives; 2,4-DNP as carbonyl test |
| Hydride reduction | NaBH₄ (mild) or LiAlH₄ (strong) | Aldehyde → 1° alcohol; ketone → 2° alcohol |
| Grignard addition | RMgBr (then H₂O/H⁺) | New C–C bond; alcohol after workup |
| Wittig | Ph₃P=CHR | Alkene (replaces C=O with C=C) |
Takeaways
- Mild acid (~pH 5) balances amine nucleophilicity with good –OH leaving.
- Acetals protect carbonyls from strong base/hydride; remove with aqueous acid.
- Cyanohydrins, hydrazones, oximes, and 2,4-DNP are reversible derivatizations; Grignard and hydride are not.
- Wittig cleanly converts C=O to C=C with predictable substitution.