Conformational properties of 1,3-difluoropropane

The conformational energy order of 1,3-difluoropropane is identified as GG < AG < AA < GG' at various ab initio calculation levels. This result is ana lyzed on the basis of the molecular structures, partial charge distribution s, and a molecular mechanics calculation. It is demonstrated that a strong dipole-dipole interaction between the highly polarized C-F bonds is the dec isive factor determining the conformational energy preference between two g auche-gauche conformers (GG and GG'). This observation suggests that, in ad dition to the gauche effect, the intramolecular electrostatic interaction s hould be considered for studying conformational behaviors of molecules with highly polarized bonds in general. The conformational energies obtained in this work propose a challenge to earlier interpretations of experimental d ata for 1,3-difluoropropane.