model pyrrole thiophene furan

These are 5-membered heterocycles whose heteroatoms are nitrogen, sulfur, and oxygen. They are aromatic systems (they comply with Hückel's rule), with thiophene being the one with the highest stabilization energy (more aromatic), followed by pyrrole, with furan being the least aromatic due to the strong electronegativity of oxygen that makes delocalization of oxygen difficult. the electronic cloud.

pyrrole thiophene furan

pyrrole

thiophene

furan