The electronic structure of 1,3-dipoles: spin-coupled descriptions of nitrone and diazomethane

Abstract

Spin-coupled theory is applied to the four π electrons of the 1,3-dipoles nitrone and diazomethane. The orbitals for both molecules take the form of distorted out-of-plane 2p functions, but one of the orbitals in nitrone is delocalized over two centres. The description is dominated by one mode of coupling of the electron spins. The calculations are compared with CAS SCF and GVB descriptions, and with projections of MO wavefunctions onto VB structures. We find no evidence for the supposed dominance of singlet diradical structures. The spin-coupled description of diazomethane is especially novel. The new features found for this molecule may hold the key to understanding the electronic structure of a number of “difficult” systems such as NO 2 and ozone.