Question

The major product of the following reaction is:
$Ph-C(=O)-CH_2CH_2-CN$
(i) $CH_{3}MgBr (excess) (ii) H_{+}H_{2}O$

• A. \(Ph-CH(CH_3)-CH_2-COCH_3\)
• B. $Ph-C(CH_3)(OH)-CH(CH_3)_2$
• C. $Ph-CO-CH_2CH_2CH_3$
• D. $Ph-CH(CH_3)-CH_2-CN$

Hint:

Grignard reagents attack both carbonyl and nitrile groups; nitriles give ketones, while aldehydes/ketones give alcohols after hydrolysis.

Answer 1

The Correct Option is A

The starting material is a substituted aryl ketone featuring a terminal cyano group. The reaction involves treatment with excess CH₃MgBr (Grignard reagent) followed by acidic hydrolysis.

Step 1: Grignard Addition to Ketone
The methyl group from CH₃MgBr nucleophilically attacks the carbonyl carbon of the ketone. Subsequent hydrolysis yields a tertiary alcohol.

Step 2: Grignard Reaction with Nitrile
Due to the use of excess Grignard reagent, it also reacts with the nitrile (–CN) group, forming an imine intermediate. Hydrolysis of this imine produces a ketone.

Overall Transformation:
- The initial ketone carbonyl is converted to a tertiary alcohol: Ph-C(OH)(CH₃)-CH₂-CH₂-CN
- The nitrile group (–CN) is transformed into a ketone: -CH₂-COCH₃

Following tautomerization or rearrangement, the final product obtained is:
Ph-CH(CH₃)-CH₂-COCH₃, corresponding to option (1).