In pyrrole, the lone pair of electrons belonging to the nitrogen is part of the aromatic ring. However, in pyridine it is part of an sp2-hybridized orbital. Why can't it be in the p-orbital and take part in the aromatic ring?
I mean, why can't the lone pair in pyrrole be in the p-orbital, with the sp2-hybridized orbital (which is not bonded to anything) sporting a single electron?
I'm not talking about the nitrogen atom having two p-orbitals participating in the aromatic ring. That would be strange. I wonder why the existing p-orbital of N cannot carry two electrons, the way it does in pyrrole.
P.S. A related question, with a very interesting answer: sp2-hybpidization in pyridine and pyrrole