Question

Tautomerism is exhibited by:
This question has multiple correct options.
(A) ${(M{e_3}CCO)_3}CH$
(B)
(C)
(D)

Answer 1

Tautomers are isomers of a compound which differ only in the position of the protons and electrons. Molecules that exhibit tautomerism have the same molecular formula and they interconvert rapidly.

Complete answer:
Tautomerism is exhibited by those compounds which have $\alpha -$ hydrogen atoms. The $\alpha -$ carbon in an organic molecule refers to the first carbon atom that attaches to a functional group, such as a carbonyl group. A hydrogen atom attached to an $\alpha -$ carbon atom is called an alpha-hydrogen atom. In tautomerism, there is an exchange of a hydrogen atom between two other atoms while forming a covalent bond to either one.
Now, if we look in the above given options, we can see that in option A,

there is one $\alpha -$ hydrogen atom in ${(M{e_3}CCO)_3}CH$ . While in option B and option D, there are two $\alpha -$ hydrogen atoms.

There is no $\alpha -$ hydrogen atom present in option C.
Hence, tautomerism is exhibited by compounds of option A, option B and option D.
The $\alpha -$ hydrogen atoms are represented using star marks and they enable the compounds to show keto-enol tautomerism.
To exhibit tautomerism, a compound must contain polar molecules and weak acidic functional groups. Tautomerism provides more stability to a compound. Tautomerism is a reversible process. Some examples of tautomerism are keto-enol, enamine-imine, lactam-lactim configurations etc.

Note:
Tautomerism involves proton transfer in an intramolecular fashion. Tautomerism has no effects on bond length or any such features. Tautomerism generally occurs in planar or non-planar molecules. Students should be careful not to confuse tautomers with depictions of "contributing structures" in chemical resonance. Resonance structures are merely convenient depictions and do not physically exist.