5 - methyl -2 -hexanone can be synthesised from acetoacetic ester and RX. Which of the following RX is used ?

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${({CH}_{3})}_{2} CHBr$

${({CH}_{3})}_{2} {CHCH}_{2} {CH}_{2} Br$

${CH}_{3} {CH}_{2} {CHBrCH}_{3}$

${({CH}_{3})}_{2} {CHCH}_{2} Br$

answer is B.

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Detailed Solution

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Explanation:

Structure of 5-Methyl-2-Hexanone:

The compound is a ketone with the structure:

CH₃-CO-CH₂-CH(CH₃)-CH₂-CH₃

It has a methyl group at position 5 of the chain.

Synthesis using Acetoacetic Ester:

The acetoacetic ester method involves:
- Alkylation of the alpha-carbon of acetoacetic ester using a suitable alkyl halide ($ RX $).
- Subsequent hydrolysis and decarboxylation yield the desired ketone.
To introduce the methyl group at position 5, the alkylation step should use isopropyl bromide ($ CH_3CHBrCH_3 $).
This ensures the correct methyl-substituted carbon chain in the final product.

Answer: The alkyl halide ($ RX $) used is isopropyl bromide ($ CH_3CHBrCH_3 $).

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