Is methyl pyrrole non-aromatic, and 1-methyl-2,5-dihydro-1H-pyrrole aromatic?

Question

I am not sure if I am counting pi electrons correctly. Or are they both aromatic, with 6 and 2 pi electrons respectively?

Answer 1

Methyl pyrrole is aromatic. No matter at what position the methyl group is you have 4 pi electrons from the 2 double bonds, and 2 from the electron pair of nitrogen (4+2=satisfying Huckel's rule), and the molecule is planar.

1-methyl-2,5-dihydro-1H- pyrrole is definitely not aromatic. It doesn't matter how many electrons it has; 2,5-dihydro means that these carbon atoms have sp3 hybridization and one of the double bonds has been reduced. Reduction happens in such a way that H goes to positions 2 and 5 and the remaining double bond is formed between positions 3 and 4. Thus you don't even have a conjugated system and there is no point in talking about aromaticity.

By the way 1H simply means that N has also sp3 hybridization and since it is forming 3 single bonds (2 for the ring and 1 with the methyl group) it is not charged.

Answer 2

well if you at Huckel rule, I'd say that methyl pyrrole is aromatic, however I think that the methyl group won't allow for the molecule to be planar. your 2nd compound is definitely not aromatic, since you have two substituents on the N, one of your extra substituents will make a bond with one of the free electrons on N, thus giving N a positive charge, thus the compound will lose it's aromaticity. B/c it's N lone pairs that allow for the the delocalization of electrons in the ring.

Answer 3

N-methyl Pyrrole