A computational analysis of the electrostatic potentials and relative bond strengths of hydrazine and some of its 1,1‐dimethyl derivatives

We have carried out a computational study of hydrazine and five of its 1,1‐dimethyl derivatives, focusing on their electrostatic potentials and relative bond strengths. Our approach has involved the calculation of ab initio self‐consistent‐field molecular orbital wave functions and molecular properties using the GAUSSIAN 82 system of programs. The electrostatic potentials of the hydrazines possess negative regions of varying sizes and strengths associated with the nitrogens of the α‐diamino linkages. Through an analysis of the positions of the most negative potentials of these regions, we have obtained directly the dihedral angles between the nitrogen lone pairs in these systems. Our use of the electrostatic potential to obtain these angles is a direct and general approach, in contrast to indirect procedures used in the past. We find this dihedral angle to be close to 90° in hydrazine, with variations in the substituted hydrazines that depend on the nature of the substituents. A highly polar structure is found for 1‐chloromethyl‐1‐methylhydrazine, which involves a delocalization of electronic charge from the substituted nitrogen towards the CH₂Cl group. We find that substituents able to withdraw significant amounts of electronic density from the central nitrogen lone pair regions, either through resonance or by induction, have a slight bond strengthening effect on the central N‐N bond. This is attributed to a decrease in the repulsion between the weakened nitrogen lone pair regions. The difficulties encountered in seeking the controlled oxidation of hydrazine to nitro derivatives may be due, in part, to the fact that two factors which would favor this, highly negative nitrogen potentials and strong N‐N bonds, are opposing in nature.