Three DNA bases exist primarily as the keto tautomer because more hydrogen bonding interactions are possible in this form. However, it was originally thought that the bases existed as the enol tautomers because they appear to be more traditionally aromatic in this form. a. Draw the aromatic enol tautomer of cytosine. b. Draw the aromatic enol tautomer of guanine. c. Draw the aromatic enol tautomer of thymine.

The scheme of the tautomers of cytosine, guanine and thymine are found in the attached file

Explanation:

The primary imine-amine tautomerism occurs in heterocyclic compounds where hydrogen may be forming the amino group (primary amine form) or migrate to adjacent nitrogen (imine form), may occur in some nitrogenous bases such as cytosine. Thymine shows double lactam-lactymal tautomy (where hydrogen migrates from the nitrogen atom to the oxygen atom of the heterocycle oxo group (lactam form) and vice versa (lactose form)), and guanine and cytosine can both.

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