How do you determine if a molecule can exhibit tautomeric forms?

A molecule can exhibit tautomeric forms if it has a functional group capable of rearranging its atoms and bonds.

Tautomerism is a type of isomerism where a molecule can exist in two or more structural forms that are in rapid equilibrium with each other. These forms, known as tautomers, differ in the position of a proton and the double bond. The most common form of tautomerism is keto-enol tautomerism, where a molecule can exist as either a ketone or an enol.

To determine if a molecule can exhibit tautomeric forms, you need to look for functional groups that can undergo this type of rearrangement. The most common functional groups that can exhibit tautomerism are carbonyl groups (C=O), such as those found in ketones and aldehydes, and hydroxyl groups (OH), such as those found in alcohols and phenols.

In the case of keto-enol tautomerism, the molecule must have a hydrogen atom on a carbon adjacent to the carbonyl group. This hydrogen atom is acidic and can be removed by a base, resulting in the formation of an enolate ion. The negative charge on the oxygen atom can then be delocalised onto the carbon atom, resulting in the formation of a double bond and the migration of the original double bond to form a hydroxyl group. This results in the enol form of the molecule.

In addition to keto-enol tautomerism, other forms of tautomerism can occur, such as nitroso-oxime tautomerism and amide-imidic acid tautomerism. These forms of tautomerism also involve the rearrangement of atoms and bonds, but they occur with different functional groups.

In conclusion, to determine if a molecule can exhibit tautomeric forms, you need to look for functional groups that can undergo rearrangement, such as carbonyl and hydroxyl groups, and the presence of an acidic hydrogen atom that can be removed by a base.