Show how you would add a Grignard reagent to an ester or a nitrile to synthesize
(c) pentan-2-one.

Verified step by step guidance

1. Identify the target molecule, pentan-2-one, which is a ketone. The goal is to synthesize this compound using a Grignard reagent and either an ester or a nitrile as the starting material.
2. Choose an appropriate Grignard reagent. To form pentan-2-one, the Grignard reagent should add a two-carbon chain to the starting material. Use ethylmagnesium bromide (CH₃CH₂MgBr) as the Grignard reagent.
3. If starting with an ester, select an ester that will yield the desired ketone after the Grignard reaction. For pentan-2-one, use methyl propanoate (CH₃CH₂COOCH₃) as the ester. The Grignard reagent will add to the carbonyl carbon of the ester.
4. If starting with a nitrile, select a nitrile that will yield the desired ketone after the Grignard reaction. For pentan-2-one, use propanenitrile (CH₃CH₂CN). The Grignard reagent will add to the carbon of the nitrile group, forming an imine intermediate, which is then hydrolyzed to the ketone.
5. Perform the reaction: (1) React the Grignard reagent with the ester or nitrile under anhydrous conditions to form the intermediate. (2) For the ester, the intermediate will collapse to form the ketone directly. For the nitrile, hydrolyze the imine intermediate with aqueous acid to yield the ketone, pentan-2-one.

Key Concepts

Grignard Reagents

Grignard reagents are organomagnesium compounds represented as R-MgX, where R is an organic group and X is a halogen. They are highly reactive nucleophiles that can add to electrophilic carbonyl groups, such as esters and nitriles, facilitating the formation of new carbon-carbon bonds. Understanding their reactivity is crucial for synthesizing ketones and other carbonyl compounds.

Ester Reactivity

Esters are organic compounds characterized by the functional group RCOOR', where R and R' are hydrocarbon chains. They can undergo nucleophilic addition reactions with Grignard reagents, leading to the formation of tertiary alcohols after hydrolysis. Recognizing the mechanism of this reaction is essential for synthesizing ketones like pentan-2-one from esters.

Nitrile Reactivity

Nitriles are compounds containing the cyano group (-C≡N) and can also react with Grignard reagents. When a Grignard reagent adds to a nitrile, it forms an intermediate imine, which can be hydrolyzed to yield a ketone. This pathway is significant for synthesizing ketones, providing an alternative route to the desired product.