Answer :
Final answer:
The compound that cannot be prepared by the reaction of a Grignard reagent with a given compound is CH₃CH₂MgX. Therefore, correct option is 4.
Explanation:
Grignard Reagent Reaction with Compounds
The Grignard reagent is widely used in organic chemistry to form carbon-carbon bonds. It is a strong nucleophile and reacts with electrophilic carbon atoms, particularly those present in carbonyl groups. The general preparation of a Grignard reagent involves the reaction of an alkyl halide with magnesium in the presence of an ether solvent, such as diethyl ether or THF.
From the options provided, it's evident that CH₃CH₂MgX cannot be prepared by the reaction of a Grignard reagent with a given compound, as it is already a Grignard reagent itself. Grignard reagents react with carbon dioxide to produce carboxylates, which upon acidification yield carboxylic acids. They can also be added to aldehydes and ketones to form alcohols.
Therefore, all the compounds listed except CH₃CH₂MgX could theoretically be prepared by the reaction of a suitable Grignard reagent with an appropriate carbonyl compound, followed by acidification if necessary. Notably, functionality that would be incompatible with Grignard reagents, such as O-H, N-H, S-H, or C=O, must be absent from the halide precursor. Moreover, halide reactivity for the formation of Grignard reagents increases in the order: Cl < Br < I.
