Studies on the molecular structures, vibrational spectra and thermodynamic properties of organic nitrates using density functional theory and ab initio methods

Abstract

The molecular structures, vibrational spectra, standard thermodynamic functions and heats of formation of methyl nitrate, ethyl nitrate, propyl nitrate, isopropyl nitrate, butyl nitrate, ethylene glycol dinitrate and nitroglycerin have been calculated at the levels of HF, MP2 and B3LYP theories in conjuction with the 6-31G* basis set. The molecular geometries and scaled frequencies calculated at the MP2 and B3LYP levels are comparable to the available experimental results in gas phase, and furthermore, the B3LYP results are slightly better than the MP2 results. The standard thermodynamic functions of NEs increase while the total energies decrease at constants with increasing number of carbon atoms and ONO2 groups in molecules. The heats of formation obtained from the isodesmic reactions at the B3LYP and HF levels and from the atomization reactions at the B3LYP level are in reasonable agreement with the experimental results. The average absolute deviations are 4.21, 7.72 and 8.47kJmol−1, respectively. But the heats of formation obtained from the atomization reaction at the HF and MP2 levels are much too higher.