Textbook problem 6.21

[Madison Kiggins 1E]

Hello, for the structure thymine, it states that it can accept 2 protons, one on each nitrogen. I was wondering why the oxygen atoms with lone pairs cannot accept protons as well.

[jennaj3k]

Oxygen is more electronegative than Nitrogen so it's unlikely to share its electrons. If it did, then thymine would have a positive charge which isn't stable. Nitrogen is less electronegative and more likely to share its electrons, so its going to accept those protons.