Organic Chemistry MCAT Practice Exam

What happens during tautomerism between the keto and enol forms?

1. Hydrogen is added

2. Constitutional isomers are formed

3. They are stereoisomers

4. Enzymes facilitate the process

The correct answer is: Constitutional isomers are formed

During tautomerism, specifically between the keto and enol forms, the reaction involves the interconversion of these two forms, which are classified as constitutional isomers. Constitutional isomers are molecules that have the same molecular formula but differ in the connectivity of their atoms. In the case of keto-enol tautomerism, the keto form features a carbonyl group (C=O), while the enol form has a hydroxyl group (-OH) bonded to a carbon-carbon double bond (C=C). This shift in bonding rearrangement signifies a change in molecular structure and connectivity, making them constitutional isomers. The process does not involve adding or removing hydrogen, nor does it involve the formation of stereoisomers. While enzymes can facilitate the conversion of keto to enol forms in certain biochemical reactions, this is not a defining characteristic of the tautomerism itself. Thus, the correct understanding of tautomerism focuses on the structural differences that categorize keto and enol forms as constitutional isomers.