Answer :
In the context of organic chemistry, Grignard reagents are versatile organometallic compounds typically used to form carbon-carbon bonds. They are characterized by the general formula [tex]\text{R-Mg-X}[/tex], where [tex]\text{R}[/tex] is an alkyl or aryl group, and [tex]\text{X}[/tex] is a halogen. Grignard reagents react with a variety of electrophilic functional groups to form alcohols after a subsequent acidic or protic work-up.
Let's consider the given options:
Ketone: Grignard reagents react with ketones to form tertiary alcohols. The carbonyl carbon of the ketone is attacked by the nucleophilic carbon in the Grignard reagent, forming a new carbon-carbon bond. After the protic work-up, an alcohol is formed.
Aldehyde: Similarly, aldehydes react with Grignard reagents to form secondary alcohols through a similar mechanism where the carbonyl carbon is attacked, followed by protonation in a work-up.
Ester: When an ester is treated with two equivalents of a Grignard reagent, the ester is first converted into a ketone and then immediately reacts further to give a tertiary alcohol after the usual protic work-up.
Epoxide: Grignard reagents also react with epoxides, opening the epoxide ring and, following the protic work-up, yield alcohols. The reaction generally takes place at the less substituted carbon atom due to the ring strain in epoxides.
Nitrile: Grignard reagents react with nitriles to form ketones, not alcohols. The Grignard reagent adds to the carbon of the nitrile group, and after hydrolysis, it results in a ketone. This step does not lead to the formation of an alcohol.
Given the options, the functional group nitrile does not afford an alcohol when treated with a Grignard reagent followed by a protic work-up.
In conclusion, the correct choice is nitrile, as its reaction with a Grignard reagent ultimately forms a ketone, rather than an alcohol.
