Question 6.21 from textbook

[Lynne Xu 3K]

Question 6.21 in the textbook asks:

The two strands of the nucleic acid DNA are held together by hydrogen bonding between four organic bases. The structure of one of these bases, thymine, is shown below.
(a) How many protons can this base accept?

In the answer key, it says only the nitrogens can accept extra protons. Why can't oxygen accept any protons?

I'm not too sure if these have any relation, but if the oxygens on thymine can't accept a hydrogen/form bonds, why are ligands such as water able to form bonds?

[jennaj3k]

Oxygen isn't accepting protons because it is much more electronegative than Nitrogen. If it did accept protons, the thymine would have an overall positive charge and be more unstable. Oxygen is unlikely to share electrons in this case. Nitrogen is more likely to share its electrons and accept protons.

[Ishant Goel 2D]

Oxygen will hold onto its electrons because it is more electronegative than nitrogen. That's why nitrogen can accept electrons and oxygen can not.

[Omar Alami 3H]

Hi,

The oxygen won't be able to accept to protons because of its higher electronegativity in comparison to Nitrogen. This higher EN means that it is much less likely for oxygen to give up an electron and share.