Question

59. Which of the following is not an active methylene compound?
A. Diethyl malonate
B. Acetoacetic ester
C. Cyanoacetic ester
D. Pentanoic acid
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Answer 1

Answer:

Which of the following is not an active methylene compound?

Answer-C. Cyanoacetic ester

Explanation:

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Answer 2

Pentanoic acid does not belong to the class of active methylene compounds. So option (d) is correct.

• Active methylene compounds possess a methylene group whose hydrogens are acidic.
• For the hydrogens to be acidic, that is to make them easily donatable, the methylene group must be bonded to electron-withdrawing groups on both sides.
• In diethyl malonate, the methylene group is flanked by two ester linkages(containing electronegative oxygen atoms) on both sides. So the hydrogens are acidic.
• In acetoacetic ester, the methylene group is bonded to the keto group on one side and an ester on another side. Both keto and ester groups are electron-withdrawing and hence the hydrogens are acidic.
• Cyanoacetic ester has a methylene group flanked by a cyano group on one side whereas the other side has an ester group. Both the groups are electron-withdrawing and the hydrogens are acidic.
• Pentanoic acid has no active methylene groups as there is only one carboxylic acid group present adjacent to the methylene group.