In the first step of a specific-base-catalyzed dehydration, a base removes a pro

Question

In the first step of a specific-base-catalyzed dehydration, a base removes a proton from the hydrate. What is the next step in this mechanism?

Please choose A, B, C, D, or E! Thanks so much!

A) negative charge from oxygen forms a double bond and hydroxide departs as a leaving group B) hydroxide departs as leaving group and a carbocation is created C) electron pair from  OH bond forms a double bond and a carbanion is created D) electron pair from OH bond moves to the oxygen atom and the oxygen atom has a negative formal charge E) negative charge from oxygen forms a double bond and the oxygen atom departs as a leaving group

Explanation / Answer

The correct answer is D.

Because, in a base catalyzed dehydration the removal of a proton is followed by the formation of the C=C pi bond and breaking of the bond with the leaving OH group. Negative charge of carbanion created by the base form the double bond and not due to the negative charge of oxygen, which rules out a, c nd e. Further on departure of leaving group carbocation is not form rather a C=C pi bond is form, hence, b is also ruled out. Thus we have D as an answer. The electron of negative charge forms the double bond and the hydroxide leaves with electron pair from OH bond moves to the oxygen atom and the oxygen atom has a negative formal charge.

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