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Question

Malonic ester contains an active methylene group and two hydrogen atoms of active methylene group which are easily replaced by alkyl and acyl groups in the presence of a strong base. The carbonation intermediate formed makes SN2 attack on alkyl or acyl groups. In the sequence of reactions given above, the final product [S] is :

44850_c5d79c5b08764b75b3637a07326c918e.png

A
CH2=CHCH2CH2COCOOH
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B
CH2=CHCH2COCH2COOH
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C
CH2=CHCH2CH2COOH
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D
CH3CH=CHCH2COOH
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Solution

The correct option is C CH2=CHCH2CH2COOH
Sodium hydride abstracts the proton from the active methylene group of diethyl malonate to obtain the carbanion [P]. This acts as a nucleophile and attacks 1-chloro pop-1-ene. Chloro group is replaced in SN2 mechanism to obtain [Q]. The ester groups are hydrolyzed in presence of acid to obtain [R].
This is followed by thermal decarboxylation to obtain [S]. Thus [S] is CH2=CHCH2CH2COOH
131067_44850_ans_10d32256894f49ec9c467c5b930e72b0.png

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