Hey guys, I got this problem wrong on a problem set and I am seeking the correct answer. It's the picture attached. The question is: which is the most basic?
The bottom nitrogen in each case is the most basic atom. So when you protonate the first structure, you'll get resonance among the two nitrogens & carbon. When you protonate the second one, you'll get the same, but you'll also have a resonance structure in which both the nitrogens have a positive charge, and the oxygen has a negative charge. The final structure possess that Sulfur atom, and I thought when you protonated the nitrogen, the sulfur would pull on the nitrogen's electrons leading to instability. But there's resonance with the sulfur, so I'm not sure.
Answer was: Last structure is most basic, middle is least basic.
And you can't use pKa values.