Quantum Mechanical and Molecular Mechanics (MM3) Studies of Hydrazines

Abstract

The structures, conformational energies, and vibrational frequencies of hydrazines have been studied at 6-31G** MP2 and 6-31G** B3LYP levels. Our theoretical structures generally agree with the available experimental data. However, our theoretical NN bond length for tetramethylhydrazine is 1.436 A at the 6-31G** MP2 level, indicating that the experimental NN distance (1.401 A) is too short. We confirm that the ab initio NN bond length strongly depends on the torsional angle even at the correlated levels. The NN bond lengths are much longer in the syn and anti conformations of 1,1-dimethylhydrazine than that in the gauche conformation. MM3 parameters for hydrazines have been optimized to reproduce experimental or quantum mechanical structures, energies, and vibrational frequencies. The bond lengthening resulting from lone-pair repulsion was accounted for with a torsion−stretch interaction. The heats of formation for hydrazines were calculated via both MP2 and MM3 methods. The optimized MM3 force field was ...