Question

Identify the combination of compounds that undergo aldol condensation followed by dehydration to produce but$-2-$enal.

• A. methanal and ethanal
• B. two moles of ethanal
• C. methanal and propanone
• D. Ethanal and propanone
• E. two moles of ethanol

Answer 1

Answer: (B)

two moles of ethanal

Reversing the process of aldol condensation in the following manner, we get two moles of ethanal.

$\underset{But-2-enal}{C{H}_{3}CH=CHCHO}\underset{Hydration}{\overset{H_{2}O}{\to }}\underset{\begin{array}{c}\beta -\text{hydroxy aldehyde}\\ \text{or aldol}\end{array}}{C{H}_3\stackrel{OH}{\stackrel{|}{C}H}-C{H}_{2}CHO}$ $\underset{Reversing}{\overset{}{\to }}\underset{Ethanal}{2C{H}_{3}CHO}$

Thus, the combination of compounds to give the given product is two moles of ethanal.