Computational Evaluation and Comparison of Some Nitramine Properties

A computational study of six nitramines, R/sub 1/R/sub 2/NNO/sub 2/, has been carried out with the objective of gaining a better understanding of how the properties of the NNO/sub 2/ group are affected by the natures of R/sub 1/ and R/sub 2/. An ab initio SCF procedure was used, with the initial step being the determination of each molecule's optimized geometry. This was subsequently used to compute its bond orders, dipole moment, and electrostatic potential. In most instances, the NNO/sub 2/ portions of the molecules are planar, due to the strong electron-withdrawing effect of the nitro group; the amino-type nitrogen can better respond to this when in a planar configuration. One consequence is that the N-NO/sub 2/ bonds possess some degrees of double bond character; their bond orders range from 1.36 to 1.63, with the weaker bonds corresponding to the more electron-withdrawing R/sub 1/ and R/sub 2/ groups. The strong negative electrostatic potentials normally associated with the lone pairs of amino-type nitrogens are greatly weakened or eliminated in most of these molecules; several of them show evidence of significant hyperconjugation, resulting in enhanced acidic character.