AB initio molecular orbital studies on 1-fluoropropane

Abstract

Geometries for both gauche and trans conformers of 1 -fluoropropane have been optimized using restricted Hartree-Fock formalism with 4-31G and 6-31G ** Gaussian basis sets. The asymmetric torsional potential energy profile for rotation of the CH 2F group has been computed at the HF/ 4-31G level and expanded as a truncated Fourier cosine series. Additional single point calculations have been carried out for both minima and saddle points at the HF/6-31G **, MP2(FULL)/431G//HF/4-31G and MP2(FULL)/6-31G **//HF/6-31G ** levels. Regardless of the level of theory used in calculation, gauche appears to be the more stable conformer with the trans-gauche energy difference varying from 1.08 to 2.21 kJ mol −1. According to the calculations the gauche → trans torsional barrier is estimated to be between 17.0 and 19.2 kJ mol −1 and the barrier separating the equivalent gauche forms between 18.6 and 20.3 kJ mol −1. A vibrational analysis based on ab initio 4-31G calculated force field is given for both conformers and compared with previous matrix isolation results.