Why is C4H4S (thiophene) aromatic?
1 Answer
Thiophene is aromatic because it has six π electrons in a planar, cyclic, conjugated system.
Explanation:
The structure of thiophene is
At first glance, it appears that thiophene has only four π electrons in a butadiene system, plus an
However, if the sulfur atom re-hybridizes to
This gives a planar, cyclic, conjugated system that contains six π electrons.
According to Hückel's rule, then, thiophene is an aromatic compound.
The resonance energy of thiophene is 122 kJ/mol.
This is less than the resonance energy of benzene (152 kJ/mol), because the
We can see this in a contour plot representing the electron density of thiophene
(from quantumwise.com)
The red colors show that the higher electron density is in the carbon portion of the molecule.
