amphoteric behavior of thymine

[Jina Bae 2G]

How does the nitro- group in thymine show amphoteric behavior? How do we know in a structure that it can readily lose a proton?

[Emily Carvalho 1C]

The nitro group is amphoteric because there is a lone pair on the Nitrogen so it can accept a proton(H+). Hydrogen bonded to electronegative atoms like nitrogen often have acidic protons that can easily dissociate. Another thing that can help you decide if a structure will lose a proton is if there is resonance.

[Annabelle Jeon 3K]

So amphoteric means that a substance can act as both an acid and base using the bronsted lowry or lewis definition. So we should look for whatever part of the molecule can both accept/donate electrons or protons.

1. identifying the base -- look for an atom that would allow for the donation of electrons aka something with lone pairs.
We can idenitfy this to be nitrogen since it has three bonds and therefore should have a lone pair if we draw out the lewis structure

2. identifying the acid -- look for an atom that would allow for the acceptance of electrons aka something with hydrogen or positive charge.
The nitrogen is attached to a hydrogen, which can accept electrons. In a similar fashion, it can donate a hydrogen proton, so it acts as an acid under both definitions.