Organic Chemistry MCAT Practice Exam

Which of the following increases the acidity of a compound?

1. Proximity to electronegative groups

2. Increase in carbon chain length

3. Decrease in molecular weight

4. Higher number of carbon substituents

The correct answer is: Proximity to electronegative groups

The increase in acidity of a compound is significantly influenced by the presence and proximity of electronegative groups. Electronegative groups, such as halogens, can stabilize the negative charge that forms when a proton is removed from the acidic proton of a compound. This stabilization occurs through electron-withdrawing effects, which diminish electron density around the acidic site. As a result, the compound becomes more willing to donate a proton, thus increasing its acidity. In contrast, factors like an increase in carbon chain length, a decrease in molecular weight, or a higher number of carbon substituents typically do not enhance acidity. The increase in carbon chain length does not inherently correlate with increased acidity, as longer chains generally contain more hydrocarbons without additional features to stabilize the negative charge. Decreasing molecular weight can affect molecular properties, but it does not directly correlate with acidity. Lastly, more carbon substituents often lead to steric hindrance and can sometimes destabilize the conjugate base, thus reducing acidity rather than enhancing it. Focusing on the influence of electronegative groups clearly illustrates their role in increasing acidity through effective charge stabilization, making proximity to these groups a key factor in acidity behavior.