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Question enter image description here

Doubt

The answer is given B. But why cant it be C after all formation of cyclopropane would increase angle strain?

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  • $\begingroup$ Where are the most acidic hydrogens? $\endgroup$
    – Waylander
    Apr 30, 2020 at 15:55
  • $\begingroup$ At adjacent site of C=O. But how come compound B is stable . I mean in E2 first Cl- should leave and after that OH- abstracts proton, but it seems here than it is following E1cb? $\endgroup$ Apr 30, 2020 at 18:22
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    $\begingroup$ [3] rings are reasonably stable, lots of examples of them. $\endgroup$
    – Waylander
    Apr 30, 2020 at 18:32

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The first thing you notice is an alcoholic base reacting with a molecule. The base looks for the most acidic hydrogen in the molecule. Since the no.of moles of $alc.KOH$ is not mentioned, we go for both the acidic hydrogens at the adjacent positions to the carbonyl functional group. Once the acidic hydrogens are abstracted, it's a simple elimination of $Cl$ that will happen.

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I agree with the comment made by @Waylander as there are plenty of examples with three-membered rings. Well, (c) is not possible but you can say (a) is a possibility. Of course (a) forms too by a simple elimination reaction but the most probable one is the abstraction of acidic hydrogen in the molecule. The stability of [3]rings can be brought about by banana bonds.

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