C-13 NMR-STUDIES OF HYDROCHLOROFLUOROPROPANES AND CHLOROFLUOROPROPANES

C-13 NMR chemical shifts of 3,3-dichloro-1,1,1-trifluoropropanes (CF3- CXY-CHCl2), 3-chloro-2,2,3,3-tetrafluoropropanes (CCIF2-CF2-R), and di astereomers of 1,3-dichloro-1,1,2,3-tetrafluoropropane were studied by analysis using MNDO calculations. In CF3-CXY-CHCl2, C-13 NMR chemical shifts of the methylene group are dependent on the electronegativity of the atoms attached to the methylene carbon, and those of the triflu oromethyl group depend on the magnetic anisotropy of neighboring halog en atoms X and Y. In CCIF2-CF2-R, the magnetic anisotropy of the atoms gauche to the terminal group and the steric effect of the terminal gr oup are responsible for the C-13 NMR chemical shift of a terminal halo genated methyl group, and the inductive effect of the substituent R ma inly determines the C-13 NMR chemical shift of the difluoromethylene g roup. (C) 1997 Elsevier Science S.A.