科研之友
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摘要
The effects of an external electric field on the C/N-NO2 bond with C/N-H and N-O bonds in CH3NO2 or NH2NO2 were compared using the DFT-B3LYP and MP2 methods with the 6-311++G(2d,p) and aug-cc-pVTZ basis sets. The results show that such fields have a minor effect on the C-N or C-H bond but a major effect on the N-O bond in CH3NO2, while in NH2NO2 electric fields affect the N-N bond greatly but the N-O or N-H bond only slightly. Thus, in CH3NO2, oxygen transfer or unimolecular isomerization to methyl nitrite might precede breaking of the C-N bond in the initial stages of decomposition, and the N-O bond could be the trigger bond in electric fields. In NH2NO2, however, N-N bond rupture may be preferential in an electric field and, consequently, the N-N bond might always be the real trigger bond. Atoms in molecules and natural bond orbital delocalization analyses, together with examination of shifts in electron density and frequencies support the above viewpoints. Forty-eight good linear correlations were found along the different field orientations at different levels of theory, including those between field strength (E) and changes in N-O/N-N bond length (Delta(RN-O/N-N)), rho((N-O/N-N)) values [Delta rho((N-O/N-N)), or stretching frequencies of the N-O/N-N bond (Delta upsilon(N-O/N-N)).
