The origin of the long N-N bond in N 2O 2: an ab initio valence bond study

Abstract

The results of some ab initio valence bond calculations, with an STO-5G basis set, are reported for the Ca 2v isomer of N 2O 2. The existence of a very long N-N bond in this isomer is calculated to be associated mostly with the nature of the hybridization and the orientation of the lone-pair atomic orbitais on each nitrogen atom. The optimum forms of the two orbitais have a large 2 s component, and overlap appreciably when the N-N internuclear separation is close to that of a normal single bond. The associated strong non-bonded repulsions that exist between the nitrogen lone-pair electrons lengthen the N-N bond. At N-N distances close to the equilibrium value (2.237 Å), the orbitals that form the N-N σ bond are almost entirely 2 p in character, and oriented at right angles to the N-O bond axes. Although some delocalization of oxygen lone-pair electrons of the Lewis structure ▪ does occur, thereby generating a fractional N-N σ bond, this effect produces only a small lengthening of the N-N bond.