Q2. Which sequence correctly ranks the following protons in order of increasing acidity?

Background

Topic: Acidity of Protons in Organic Molecules

This question tests your understanding of how structural features and functional groups affect the acidity of different protons in a molecule. You need to compare the acidity of protons labeled 1, 2, and 3 in the given bicyclic ketone structure.

Key Terms and Concepts:

• Acidity: The tendency of a proton (H+) to dissociate from a molecule. More acidic protons are more easily removed.

• Inductive Effect: Electron-withdrawing groups (like carbonyls) increase acidity by stabilizing the negative charge on the conjugate base.

• Resonance Effect: Protons adjacent to groups that can delocalize charge (like carbonyls) are often more acidic.

• Hybridization: Protons attached to sp2 or sp hybridized carbons are generally more acidic than those on sp3 carbons.

Step-by-Step Guidance

1. Examine the structure and identify the environment of each labeled proton (1, 2, and 3). Consider their proximity to the carbonyl group and the ring system.

2. Recall that protons closer to electron-withdrawing groups (like the carbonyl) are typically more acidic due to stabilization of the conjugate base.

3. Analyze whether any of the protons are alpha to the carbonyl (directly adjacent), which would increase their acidity via resonance stabilization.

4. Consider the hybridization of the carbon atoms to which each proton is attached. Protons on sp2 carbons are more acidic than those on sp3 carbons.

5. Rank the protons based on your analysis, from least acidic to most acidic, but stop before assigning the final sequence.

Try solving on your own before revealing the answer!