One mole of acetone is condensed with two moles of benzaldehyde in the presence of dilute $NaOH$ to give dibenzalacetone, $C X_{6} H X_{5} CH = CH - CO - CH = CH - C X_{6} H X_{5}$ . Counting only the elimination steps of the mechanism in which hydroxide is lost from a carbanion (E1cB), how many such steps occur in the formation of one molecule of the product from the aldol additions?

Answer: D

Each benzaldehyde adds to an alpha-carbon of acetone to give a beta-hydroxy ketone unit. Each of the two beta-hydroxy ketone units then loses water by E1cB through an enolate:

PhCH (OH) CH X_{2} CO X^{-}

gives

PhCH = CH - CO X^{-}

twice. The total number of E1cB steps is 2.

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Answer: D

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