Decision Framework for Carbonyl Reduction

Question to ask: What product is needed?

If you need an ALCOHOL (C-OH, oxygen retained):

• Use NaBH4 (mild, selective, works in protic solvents like MeOH)
• Use LiAlH4 (stronger, works in dry ether; also reduces esters, acids, amides)
• Use H2/Pd or H2/Pt (catalytic hydrogenation)

If you need a HYDROCARBON (CH2, oxygen completely removed):

• Need Clemmensen OR Wolff-Kishner
• Sub-question: Are there acid-sensitive groups?
  • YES → Use Wolff-Kishner (NH2NH2/KOH, basic)
  • NO → Use Clemmensen (Zn-Hg/conc. HCl, acidic) [also note: base-sensitive groups require Clemmensen]

Practical Examples

NEET Exam Tip

When asked "which reagent converts C=O to CH2" — answer is Clemmensen (Zn-Hg/HCl) or Wolff-Kishner $\frac{NH2NH2}{KOH}$. When asked "which converts C=O to CHOH" — NaBH4 or LiAlH4.