The inversion process of pyrrole, phosphole, arsole, stibole, and bismole is analyzed in detail by using ab initio and density functional techniques. The results are compared with the corresponding divinyl and diethyl compounds, HM(C2H3)(2) and HM(C2H5)(2), respectively (M = N, P, As, Sb, and l3i). The inversion barrier increases down the Group 15 elements and from the cyclic, via the divinyl to the diethyl compounds. The inversion process can be rationalized in terms of a second-order Jahn-Teller distortion using HOMO/LUMO energy differences. B3LYP calculations predict that fluorination of the pyrrole ring leads to nonplanar structures of both the tetra- and pentafluoropyrrole.