Answer
The proton on the left is more acidic.
Work Step by Step
Draw the conjugate bases:
In the first one, I am going to remove the proton on the left:
Remove the highlighted hydrogen on the left, and give a lone pair to the carbon that was connected to it (It will get a negative charge).
In the second one, I am going to remove the proton on the right:
Remove the highlighted hydrogen on the right, and give a lone pair to the carbon that was connected to it. (It will get a negative charge).
Now, check which one is more stable, use the ARIO rules:
1. Atom:
- In both structures, the negative charge is on a carbon, so there is no difference.
2. Ressonance:
- The first conjugate base will have 2 ressonance structures, and the charge will be spread between a carbon and a nitrogen.
- The second conjugate base will have 2 ressonance structures too, but the charge will be spread between 2 carbons.
- Therefore, the first base should be more stable.
- Since the first conjugate base is more stable, the proton on the left is more acidic.
