The major product of the following reaction is : Reactant: Ph-CO-CH2CH2-CN; (i) CH₃MgBr (excess); (ii) H₃O^+ 1. structure (1) 2. structure (2) 3. structure (3) 4. structure (4)

Answer: 2. structure (2) Key idea: Grignard reagent adds to both the ketone and the nitrile, but the nitrile adduct is hydrolysed to a ketone only at the work-up step. CH₃MgBr adds to the aryl ketone C=O and gives, on work-up, the tertiary alcohol mathrmPh-C(CH₃)(OH)- . It also adds to -mathrmCequivN to give an imine magnesium salt, which does not react further; H₃O^+ hydrolyses it to a methyl ketone -COCH₃ . Product is the hydroxy ketone in option (2). Option (1) leaves CN untouched, (3) would need a second Grignard addition to the ketone formed from the nitrile, which cannot happen because the imine salt is unreactive, (4) has no Grignard added to the ketone.

Topic: Aldehydes and ketones: HCN, NH3 derivatives, Grignard, oxidation, reduction (Wolff-Kishner, Clemmensen)· Organic Compounds Containing Oxygen

The major product of the following reaction is :Reactant: Ph-CO-CH2CH2-CN; (i) CH_3MgBr (excess); (ii) H_3O^+

The major product of the following reaction is :

Reactant: Ph-CO-CH2CH2-CN; (i) \(\mathrm{CH_3MgBr}\) (excess); (ii) \(\mathrm{H_3O^+}\)

Reactant PhCOCH2CH2CN with reagents, and four product structures: (1) Ph-C(CH3)(OH)-CH2CH2-CN; (2) Ph-C(CH3)(OH)-CH2CH2-C(=O)CH3; (3) Ph-C(CH3)(OH)-CH2CH2-C(CH3)2OH; (4) PhCO-CH2CH2-C(=O)CH3

1. structure (1)

2. structure (2)

3. structure (3)

4. structure (4)

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Answer: 2. structure (2)

Key idea: Grignard reagent adds to both the ketone and the nitrile, but the nitrile adduct is hydrolysed to a ketone only at the work-up step.

\(\mathrm{CH_3MgBr}\) adds to the aryl ketone C=O and gives, on work-up, the tertiary alcohol \(\mathrm{Ph{-}C(CH_3)(OH){-}}\).
It also adds to \(-\mathrm{C{\equiv}N}\) to give an imine magnesium salt, which does not react further; \(\mathrm{H_3O^+}\) hydrolyses it to a methyl ketone \(-\mathrm{COCH_3}\).

Product is the hydroxy ketone in option (2). Option (1) leaves CN untouched, (3) would need a second Grignard addition to the ketone formed from the nitrile, which cannot happen because the imine salt is unreactive, (4) has no Grignard added to the ketone.

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The major product of the following reaction is :Reactant: Ph-CO-CH2CH2-CN; (i) CH_3MgBr (excess); (ii) H_3O^+

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