Question

The compound obtained when acetaldehyde reacts with dilute aqueous sodium hydroxide exhibits:

• A. geometrical isomerism
• B. optical isomerism
• C. neither optical nor geometrical isomerism
• D. both optical and geometrical isomerism

Answer 1

The correct option is B optical isomerism

When acetaldehyde is treated with aqueous sodium hydroxide solution, it undergoes aldol condensation (because of the presence of $\alpha -H$ atom) as:
$C{H}_{3}CHO+HC{H}_{2}CHO\underset{NaOH}{\overset{Dil.aqueous}{\to }}C{H}_{3}CH\left(OH\right)C{H}_{2}CHO$(shows optical isomerism)

Since, the aldol formed contains one asymmetric carbon atom, it will show optical isomerism.

On heating, aldol loses water and gives an alkene.
$C{H}_{2}CH\left(OH\right)C{H}_{2}CHO\stackrel{\Delta }{\to }C{H}_{3}CH=CHCHO$
(shows geometrical isomerism)

The obtained alkene shows geometrical isomerism.

Option B is correct.