Determination of thermodynamic parameters of C2–C3 nitroalkanes using anharmonic oscillator approximation and explicit treatment of internal rotation

Harmonic oscillator approximation is usually used to calculate the partition function for low frequency modes that represent hindered internal rotation. Nevertheless, employing of harmonic oscillator approximation may lead to significant errors when internal rotation of functional groups in molecules corresponds to hindered or free rotation. From the other hand anharmonic oscillator approximation should be used for the proper reproduction of the energies of excited vibrational states especially at high temperatures. Therefore, we carried out present theoretical study to reveal the effect of internal rotation and anharmonic oscillator approximation on thermodynamic parameters of nitroethane, 1- and 2-nitropropane.