Structure of thionyl imides — the new isomer

Equilibrium geometries of the molecules XNSO (where X  Li, Na, HBe, HMg, H2B or H2Al) were calculated using the second-order Møller-Plesset perturbation theory. The four-membered planar cyclic form, previously postulated for a number of other pseudohalides, is predicted to be the dominant isomer in the vapour phase. Potential energy curves for the migration of the substituent between the end atoms of the NSO group were also calculated and the relative stabilities of the new structures are compared to the ‘conventional’ open chain isomers.