Hypothetical heterocyclic carbenes

Abstract Density functional theory is used to explore the geometries and properties of 55 heterocyclic carbenes containing N, P, As, Sb, Bi, O, S, Se, Te and Po. Planar and non-planar structures have been systematically evaluated and a variety of measures (including Wiberg bond indices, orbital occupancies, HOMO–LUMO gaps, proton affinities, J( 13 C– 1 H) coupling constants and isodesmic reaction energies) have been considered for all systems. The main conclusions are that the heavier heteroatoms can be effective π-donors towards the carbene carbon if planarity can be attained, and that the cost of attaining this planarity is actually quite low for the majority of the heterocyclic carbenes considered.