Organic Chemistry MCAT Practice Exam

Which functional group is more stable in its keto form than in its enol form?

1. Alcohols

2. Ketones

3. Aldehydes

4. Esters

The correct answer is: Ketones

In organic chemistry, the stability of keto and enol forms is often discussed in terms of the keto-enol tautomerism, where the keto form typically features a carbonyl group (C=O) and the enol form has a double bond (C=C) along with an alcohol group (–OH). Ketones tend to be more stable in their keto form for several reasons. The presence of the electronegative oxygen in the carbonyl group stabilizes the keto form through resonance, allowing for the distribution of electron density. Additionally, the keto form usually has a stronger bond due to the C=O bond being more polar and generally stronger than the C=C bond found in the enol form. In terms of thermodynamic stability, the keto form is often favored since it is lower in energy compared to the enol form. This is commonly observed in many ketones and is a general principle that holds true for a wide variety of ketone compounds. Other functional groups like alcohols, aldehydes, and esters can exhibit keto-enol tautomerism, but they do not show the same degree of stability in their keto forms relative to their enol forms as ketones do. For instance, aldehydes