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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3o4142

Which of the following reactions proceed by an E1cB mechanism?

A $PhSO X_{2} CH X_{2} CH X_{2} OPh$ with $NaOEt / EtOH$
B $CH X_{3} CH X_{2} CH X_{2} Br$ with $NaOEt / EtOH$
C $CH X_{3} - CO - CH X_{2} - CH (OH) - CH X_{3}$ (4-hydroxypentan-2-one) with $NaOH$ , warm
D $(CH X_{3}) X_{3} C - Br$ in warm ethanol

Answer: A, C

The sulfone and the beta-hydroxy ketone each have an acidic alpha-H and a poor leaving group, so they eliminate via a stabilised carbanion. 1-Bromopropane with ethoxide gives E2, and tert-butyl bromide in ethanol gives E1.

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