ON THE ORIGIN OF THE GAUCHE EFFECT - A QUANTUM-CHEMICAL STUDY OF 1,2-DIFLUOROETHANE

The conformational equilibrium of 1,2-difluoroethane has been investig ated using ab initio quantum chemical calculations at the SCF, MP2 and CCSD(T) levels, with ANO basis sets. The relative stability of the ga uche-conformation of 1,2-difluoroethane is found to be a consequence o f the nodal structure of the singly occupied orbital in the CFH2 radic al. It is also shown that the nodal structure of the singly occupied o rbitals in the CFH biradical can explain the stability of the cis conf ormation of 1,2-difluoroethene.