A) geometrical isomerism
B) optical isomerism
C) neither optical nor geometrical isomerism
D) both optical and geometrical isomerism
Correct Answer: B
Solution :
When acetaldehyde is treated with aqueous sodium hydroxide solution, it undergoes aldol condensation (because of the presence of \[\alpha -H\]atom) as. \[C{{H}_{3}}CHO+HC{{H}_{2}}CHO\xrightarrow[NaOH]{Dil.\,\,aqueous}\] \[\underset{\begin{smallmatrix} aldol \\ (shows\text{ }optical\text{ }isomerism) \end{smallmatrix}}{\mathop{C{{H}_{3}}CH(OH)C{{H}_{2}}CHO}}\,\] Since, the aldol formed contains one asymmetric carbon atom, it will show optical isomerism. On heating, aldol loses water and gives an alkene. \[C{{H}_{3}}CH(OH)C{{H}_{2}}CHO\xrightarrow{\Delta }\] \[\underset{(shows\text{ }geometrical\text{ }isomerism)}{\mathop{C{{H}_{3}}CH=CHCHO}}\,\] The obtained alkene shows geometrical isomerism.
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