Question

Tautomerism is not shown by:
A. $C{H_3}N{O_2}$
B. ${C_6}{H_5}COC{H_3}$
C. ${(C{H_3})_2}C = N - OH$
D. ${C_6}{H_5}CHO$

Answer 1

In order to answer this question, we should know the essential conditions for tautomerism that there should be an electronegative group atom which is bonded by a double or triple bond and one alpha-hydrogen must be present on a saturated carbon.

Complete Step By Step Answer:
Let us first understand the phenomenon of tautomerism.
It is a phenomenon in which a chemical compound exists in two or more structures which can be converted convertible into each other. The difference is only the position of hydrogen. Hence, the isomers formed are called tautomers. They have the same molecular formula but different structure formula. They convert to attain more stability of the compound. These tautomers are in equilibrium with each other.
We know that tautomerism exists in keto-enol pairs in which one structure is ketone and the other one is enol form.
In the given question, benzaldehyde i.e. ${C_6}{H_5}CHO$ does not show tautomerism as we know that the presence of alpha- hydrogen is the essential condition for tautomerism. Here in this case, benzaldehyde, there is no alpha-hydrogen atom present in the compound. Therefore, it does not show tautomerism.
Hence, the correct answer is option (D).

Note:
Always remember the essential conditions of the tautomerism phenomenon. It generally occurs due to the more stability of keto-enol form. This is the most common tautomerism. These keto and enol forms are interconvertible into each other. The most important point to be remembered is the presence of alpha-hydrogen and one electronegative group attached with carbon by double or triple bond.