4-Oxopentanal, CH3-CO-CH2CH2-CHO, is treated with exactly one equivalent of CH3MgBr at -78 degC, followed by aqueous NH4Cl. The major product is

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JEE Advanced levelSingle correct optionDifficulty 3 of 3o1091

4-Oxopentanal, $CH X_{3} - CO - CH X_{2} CH X_{2} - CHO$ , is treated with exactly one equivalent of $CH X_{3} MgBr$ at $- 78^{\circ} C$ , followed by aqueous $NH X_{4} Cl$ . The major product is

A5-hydroxyhexan-2-one
B2-methylhexane-2,5-diol
Chexane-2,5-dione
D4-hydroxy-4-methylpentanal

Answer: A

The aldehyde carbonyl is less hindered and more electrophilic than the ketone, so with one equivalent at low temperature the Grignard reagent adds mainly there, giving after work-up

CH X_{3} - CO - CH X_{2} CH X_{2} - CH (OH) - CH X_{3}

. The diol would need a second equivalent, and the other options require attack on the ketone first or oxidation.

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4-Oxopentanal, CHX3​−CO−CHX2​CHX2​−CHO, is treated with exactly one equivalent of CHX3​MgBr at −78 ∘C, followed by aqueous NHX4​Cl. The major product is

Answer: A

More questions on Nucleophilic addition to aldehydes and ketones

4-Oxopentanal, $CH X_{3} - CO - CH X_{2} CH X_{2} - CHO$ , is treated with exactly one equivalent of $CH X_{3} MgBr$ at $- 78^{\circ} C$ , followed by aqueous $NH X_{4} Cl$ . The major product is