Please verify that the pka of pyrrole is 6.04 and the pka of imidazole is 6.95. Why are they different?

Doesn't pysrrole have one more bonded H in the ring structure than imidazole? I would expect slightly more acidic behavior just on the basis of this.

To verify the pKa values of pyrrole and imidazole and understand why they are different, we can refer to experimental data and compare their molecular structures.

1. Experimental verification:
To confirm the pKa values, you can consult reliable scientific sources such as research papers, textbooks, or databases. These sources provide experimentally determined pKa values of various compounds. You can search for the specific pKa values of pyrrole and imidazole to verify their acidity.

2. Comparing molecular structures:
On the basis of molecular structure, pyrrole and imidazole do have differences that can explain their different pKa values:

- Pyrrole (C4H5N) has a five-membered ring containing four carbon atoms and one nitrogen atom. Each carbon atom is bonded to one hydrogen atom.
Structure: C=C-C-C-N
|
H

- Imidazole (C3H4N2) also has a five-membered ring, but it contains two nitrogen atoms and three carbon atoms. Each carbon atom is bonded to one hydrogen atom.
Structure: C=C-C-N
|
N
|
H

The main difference between the two structures is the presence of an additional nitrogen atom in imidazole. This nitrogen atom can participate in hydrogen bonding, making imidazole more basic than pyrrole. The electron-withdrawing nature of the second nitrogen atom in imidazole can also decrease the availability of electrons on the first nitrogen atom, making imidazole less acidic than pyrrole.

Therefore, based on the additional nitrogen atom and its electron-withdrawing effects in imidazole, we expect imidazole to be less acidic compared to pyrrole, explaining the difference in their pKa values.