Question

Which of the following Compounds does not exhibit tautomerism?
A) ${\text{C}}{{\text{H}}_3}{\text{N}}{{\text{O}}_2}$
B) ${\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{N}}{{\text{O}}_2}$
C) ${{\text{C}}_6}{{\text{H}}_5}{\text{CH = CH - OH}}$
D) ${\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{OH}}$

Answer 1

Hint: The essential condition for tautomerism is that there should be an electronegative atom present bonded by a double or triple bond and one alpha-hydrogen must be present on a saturated carbon.${\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{OH}}$ is called ethyl alcohol. It contains a single bond between carbon atoms and is a saturated molecule but does not contain alpha hydrogen. Hence it does not show tautomerism.

Step-by-Step Explanation: Tautomerism is a phenomenon in which a chemical compound exists into $2$ or more interconvertible structures which differ in the position of hydrogen. The isomers formed are called tautomers as they have the same molecular formula but different structural formula. They change to give more stability to the compound. They exist in equilibrium with each other. The most common tautomerism exists between keto-enol pairs in which one structure is ketone and the other is –enol form.
The tautomers of nitro-methane, nitro-ethane and${{\text{C}}_6}{{\text{H}}_5}{\text{CH = CH - OH}}$ is given as-
 
Here, ${\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{OH}}$ is a saturated molecule as it only has single bond so it cannot change its structure. Hence it does not exhibit tautomerism.

Hence the answer is ‘D’.

Note: Tautomerism occurs due to the more stability of keto form. Keto-enol tautomerism is the most common tautomerism. Both tautomers (keto and enol) are interconvertible into each other. It is possible only in the compounds that contain polar molecules and weakly acidic functional groups.