Theoretical study of solvent effects on the conformational preference in CH 2FWH (W=O, S) using PCM and IPCM methods

Abstract

The solvent effect on conformational stability and physical properties, such as dipole moment, chemical potential and chemical hardness in CH 2FWH (W=S, O) has been examined using HF, MP2 and B3LYP methods with the 6-311 + G(d,p) basis set by applying the polarizable continuum model (PCM) and the isodensity polarizable continuum model (IPCM). All the conformers are stabilized in going from the gas phase to solution one. Gauche conformer, the most stable conformer in the gas phase, is still the most stable conformer in the solution phase. The electrostatic contribution to the salvation energy is mainly responsible for the changes of relative energies. The results obtained with these methods reveal that the anomeric effect decreases as the dielectric constant of medium increases. The energetic preference of gauche over anti in polar solvents ( ε > 5) is greater in CH 2FSH than in CH 2FOH. Similar to the gas phase, natural bond orbital (NBO) analysis shows that the effect of electrostatic and steric contributions involved in the Lewis term on stability of gauche conformers is still less important than the charge delocalization. Furthermore, the preference of delocalization effect over electrostatic and steric effects in the solution phase is greater than the gas phase.