Question

If pyridine and pyrimidine are both aromatic compounds, how many elctrons does each nirtogen atom contribute to the electron cloud of each compound?

Answer 1

In each compound, each `"N"` atom contributes one electron to the π cloud.

Explanation:

Pyridine

The structure of pyridine is

`"N"` has a lone pair and one electron in each of the σ bonds to the carbon atoms on either side.

That leaves 1 valence electron available to participate in the aromatic π cloud.

Pyrimidine

The structure of pyridine is

The two `"N"` atoms are equivalent.

Each `"N"` has a lone pair and one electron in each of the σ bonds to the carbon atoms on either side.

That leaves 1 valence electron available in each `"N"` atom to participate in the aromatic π cloud.