Question 9.1: Thiophene, a sulfur-containing heterocycle, undergoes typica...

Accounting for the Aromaticity of a Heterocycle

Thiophene, a sulfur-containing heterocycle, undergoes typical aromatic sub-stitution reactions rather than addition reactions. Why is thiophene aromatic?

S t r a t e g y
Recall the requirements for aromaticity—a planar, cyclic, conjugated molecule with 4n + 2 π electrons—and see how these requirements apply to thiophene.