Computed Effects of Electric Fields Upon the C-NO2 and N-NO2 Bonds of Nitromethane and Dimethylnitramine

摘要

We report the results of a computational (B3PW91/6-31G**) investigation of the effects of electric fields of different strengths and directions upon some properties related to the C-NO2 and N-NO2 bonds in nitromethane, H3C-NO2 and dimethylnitramine, (H3C)(2)N-NO2. We look at the interaction energies of the fields with the molecules, the dipole moments of the latter, the lengths of the C-NO2 and N-NO2 bonds, and we particularly focus upon their stretching vibration frequencies. The field-induced frequency shifts are determined by means of a formula linking them to the dipole moment derivatives and the field strengths. This formula was derived originally for hydrogen-bonded systems, but we show that it is applicable as well to these C-NO2 and N-NO2 bonds; their predicted relative frequency shifts correlate extremely well with directly computed Delta omega(epsilon) (R-2 = 0.9992). It was found that the fields that reinforce the intrinsic H3C-NO2 and (H3C)(2)N-NO2 polarities also interact favorably energetically with the molecules and, particularly important, increase the C-NO2 and N-NO2 stretching frequencies. This presumably indicates the strengthening of these bonds. Fields in the opposite direction do the reverse. (C) 2008 Wiley Periodicals, Inc. Int J Quantum Chem 109: 3-7, 2009