[alon]

What is the basicisity difference of the nitrogens on cafffiene?
I believe that the two unpaired electrons on the nitrogen next to the double bond are more delocalized  thus this nitrogen is a better lewis base than the other two nitrogens.

[Mitch]

the nitrogen next to the double bond are more delocalized  thus this nitrogen is a better lewis base than the other two nitrogens.

That is the exact reason why it's a poor lewis base. If it gave up it's electrons it would no longer be delocalized in the ring system.

[alon]

thanks mitch