Rotational barriers in tetraformylhydrazine

Abstract

Density functional calculations are reported on the various conformations of tetraformylhydrazine. These calculations indicate that rotation about the N–N bond is a relatively high-energy process, >140 kJ mol⁻¹, but that a multi-step pathway can yield the same result with substantially lower activation barriers of ≈80 kJ mol⁻¹. The calculated differences in barrier heights are rationalised on the basis of changes in geometrical and electron density properties. This analysis indicates the barrier to rotation about N–N in each case is dominated by destabilisation of N atoms and weakening of the N–N bond, but that the balance between steric and electronic factors determines the overall barrier. The calculations also suggest possible differences in spectroscopic properties that could be used to confirm the proposed low-energy pathway.