| Reducing Agent | What It Reduces | What It Doesn't Reduce |
|---|---|---|
| NaBH4 | Aldehyde, ketone → alcohol | COOH, COOR, CONR2, C=C, C≡C, NO2 |
| LiAlH4 | Aldehyde, ketone, COOH, COOR, CONR2, C≡N, epoxide → alcohols/amines | C=C, C≡C (usually), aromatic ring |
| H2/Pd | C=C, C=O, C≡C, NO2 | Selective with proper conditions |
| Clemmensen | ArCOR → ArCH2R (C=O → CH2) | Use for acid-stable substrates |
| Wolff-Kishner | RCOR' → RCH2R' (C=O → CH2) | Use for base-stable substrates |
| MPV (Al(OiPr)3) | Ketone → alcohol (specific) | Highly selective |
Key distinction for JEE: NaBH4 is selective (only C=O of aldehyde/ketone); LiAlH4 is aggressive (reduces nearly everything). Choose based on what other functional groups are present.