(a) Why is furan aromatic? Draw a picture showing the two atomic orbitals for the two lone pairs on the oxygen, using the "side-on" view of furan below. Then, use that picture to explain why furan is aromatic, not antiaromatic. (4 points)
furan
"side-on" view
(b) Pyrrole (left) is quite aromatic. But the phosphorus analogue is much less aromatic, and the arsenic analogue is essentially non-aromatic. What might be changing, going down the periodic table, that would reduce the aromaticity of the ring? Why? (2 points)