Molecular Orbital Study of Acyclical Nitramine Compounds

摘要

The results of MNDO and MINDO/3 semi-empirical self-consistent field calculations for the ground state structures, hears of formation, and dipole moments of several acyclical nitramine compounds are compared with each other and experiment. Because the reactions of such molecules are complicated, it may happen that the first steps of their decompositions are not amenable to experimental study, and, in order to attempt to obtain an understanding of the complete dynamics, it is necessary to perform theoretical calculations. The small value of the ratio of electron to proton masses, 1/1823, leads to a decoupling of the electronic motion from that of the heavy particles, the Born-Oppenheimer approximation. The quantum mechanical treatment of the electronic motion for fixed positions of the nuclei forms the basis of quantum chemistry which generates a potential energy surface that determines the heavy particle motion classically, semi-classically, or quantum mechanically. In Sec II, the Hartree-Fock (HF) self-consistent field (SCF) method is briefly described. The reduction of the HF equations by means of atomic orbitals (AO's) is described as is the problem of multifold proliferation of matrix elements. In Sec III, the reduction of the full SCF Hamiltonian to the MINDO/3 and MNDO forms is discussed, and the empirical parameterization of matrix elements is described. In Sec. IV, the results obtained for the ground state properties of several acyclical nitramine compounds using MINDO/3 and MNDO Hamiltonians are compared with each other and with experiment.