Vibrational Spectra,Assignment,Conformational Stability and Ab initio/DFT Calculations for 1-Nitropropane

摘要

The infrared spectra (4000-400 cm~(-1)) of solid and the Raman spectra (3500-30 cm~(-1)) of liquid and solid 1-nitropropane,CH_3CH_2CH_2NO_2,have been registered.Both the trans and gauche conformers have been identified in the fluid phase,while the trans form remains in the stable solid.Temperature dependence (190-230 K) of the liquid 1-nitropropane Raman spectra has been carried out.From these data,the enthalpy difference was determined to be 870+-105 J-mol~(-1),with the gauche conformer being the more stable rotamer.Ab initio and DFT calcualtions at different levels of approximation (HF,MP2,B3LYP,B3PW91) gave optimized geometries,harmonic force fields,and vibrational frequencies for the trans and gauche conformers.All the calcualtions (except the B3PW91/6-31G~* level) predicted gauche as the low-energy conformer.Theoretical force constants are analyzed for formulating constraints in the molecular force field model of 1-nitropropane.