Which among the following compounds will give a secondary...

Which among the following compounds will give a secondary alcohol on reacting with Grignard reagent followed by acid hydrolysis? (I) HCHO (II) $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{CHO}$ (III) $\mathrm{CH}_{3} \mathrm{COCH}_{3}$ (IV) $\mathrm{HCOOC}_{2} \mathrm{H}_{5}$ Select the correct answer using the codes given below: (a) III only (b) II only (c) I and IV (d) II and IV

Which among the following compounds will give a secondary alcohol on reacting with Grignard reagent followed by acid hydrolysis?
(I) HCHO
(II) $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{CHO}$
(III) $\mathrm{CH}_{3} \mathrm{COCH}_{3}$
(IV) $\mathrm{HCOOC}_{2} \mathrm{H}_{5}$
Select the correct answer using the codes given below:
(a) III only
(b) II only
(c) I and IV
(d) II and IV

Key Concepts

Reactivity of Ketones with Grignard Reagents

Ketones have a carbonyl group bonded to two carbon groups. When a Grignard reagent attacks a ketone, the addition produces an alkoxide that, upon protonation, forms a tertiary alcohol. The presence of two alkyl groups on the carbonyl typically results in the formation of a tertiary alcohol after the reaction.

Grignard Reagent Mechanism

Grignard reagents are organomagnesium compounds that act as strong nucleophiles. They add to electrophilic carbonyl groups, forming tetrahedral alkoxide intermediates. Upon acid hydrolysis, these intermediates are protonated to give alcohols. The product type (primary, secondary, or tertiary alcohol) depends on the structure of the carbonyl compound and the number of Grignard reagent equivalents used.

Reactivity of Aldehydes with Grignard Reagents

Aldehydes have the carbonyl group bonded to at least one hydrogen. When a Grignard reagent adds to a substituted aldehyde (where the carbonyl carbon is attached to one alkyl group and one hydrogen), the nucleophilic attack yields a secondary alkoxide. After acid work-up, this gives a secondary alcohol. In contrast, if the aldehyde has two hydrogen atoms (as in formaldehyde), the alcohol formed is primary.

Reactivity of Esters with Grignard Reagents

Esters react with Grignard reagents through a two-step process. The first equivalent of the Grignard reagent adds to the ester to generate a ketone intermediate, which is more reactive than the starting ester. A second equivalent then adds to this intermediate, forming an alkoxide that, after acid hydrolysis, gives an alcohol. In cases where the ester has a hydrogen atom attached to the carbonyl (for instance, in formate esters), the final product is a secondary alcohol.

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