Quantum-Chemical Studies on Geometries of Nitrate Molecules

Semi-empirical SCF-MO calculations by MINDO/3, MNDO and AMI have been performed to obtain molecular geometries of 32 nitrates by complete optimization. The results calculated from the three methods are similar to each other. By comparing with the experimental geometries of four compounds (i.e., methyl nitrate, N- nitrobis(2-hydroxyethyl)-amine dinitrate, nitroglycerine and pentaerythrite tetranitrate), it is found that AM 1 method is better than the other methods for predicting molecular geometry. The -ONO2 groups in molecules of various nitrates have approximately the same value of geometrical parameters. The bond lengths and bond angles of straight-chain alkyl nitrates are akin to each other, and all heavy atoms in the molecules are coplanar at their trans-conformations. The bisubistituted straight-chain and tetrasubstituted ester molecules have symmetrical structures.