Abstract: An ab initio PD/LSF and (exp-6-1) model has been used to deal with intramolecular non-bonded interaction of 1,1-difluoro-ethane and 1.2-difluoroethane. It is concluded that the energy difference of isomers comes from intramolecular non-bonded inter-acion between the atoms. This model provides a useful, simple and easily understood approximation to intramolecular non-bon-ded interaction.

Key words: Intramolecular non-bonded interaction, Ab initio calculation, PD/LSF charge, (exp-6-1) model, Difluoroethane