Answer :
Final answer:
The reason a ketone reacts with a Grignard reagent to form a tertiary alcohol, while a nitrile forms a ketone, is due to different reaction mechanisms involving distinct electrophilic characters and intermediate formations. Therefore correct option is a.
Explanation:
Grignard Reactions with Ketones and Nitriles -
When a Grignard reagent reacts with a ketone, a tertiary alcohol is formed. The mechanism involves the nucleophilic addition of the Grignard reagent to the carbonyl carbon of the ketone, leading to the formation of a tetrahedral alkoxide intermediate. Upon protonation during acid work-up, a tertiary alcohol is produced.
In contrast, when a Grignard reagent reacts with a nitrile, a ketone is generated. The reaction mechanism starts with the nucleophilic attack of the Grignard reagent on the electrophilic carbon in the nitrile, forming an imine salt. This intermediate is then hydrolyzed to yield a ketone.
The different outcomes of these reactions are due to the distinct reaction mechanisms involved in each case, which can be attributed to the different electrophilic characters and subsequent intermediates formed with ketones and nitriles.
