Grignard reagent (RMgX) acts as R:- (carbanion equivalent). It adds to C=O:
| Carbonyl Substrate | Product (after H3O+) |
|---|---|
| HCHO | RCH2OH (primary alcohol) |
| R'CHO | RR'CHOH (secondary alcohol) |
| R'COR" | RR'R"COH (tertiary alcohol) |
| CO2 (dry ice) | RCOOH (carboxylic acid, after hydrolysis) |
| Ethylene oxide | RCH2CH2OH (primary alcohol, +2C) |
| R'COOR" | RR'(R)COH (tertiary, 2 eq RMgX added) |
| R'CN | R'COR (ketone, after hydrolysis of imine intermediate) |
Critical limitations: RMgX is destroyed by any acidic H source — H2O, ROH, NH3, RNH2, RCOOH, terminal alkynes. Keep all reagents anhydrous.