Add time:07/25/2019         Source:sciencedirect.com

13C NMR chemical shifts of 3,3-dichloro-1,1,1-trifluoropropanes (CF3-CXY-CHCl2), 3-chloro-2,2,3,3-tetrafluoropropanes (CClF2-CF2-R), and diastereomers of 1,3-dichloro-1,1,2,3-tetrafluoropropane were studied by analysis using MNDO calculations. In CF3-CXY-CHCl2, 13C NMR chemical shifts of the methylene group are dependent on the electronegativity of the atoms attached to the methylene carbon, and those of the trifluoromethyl group depend on the magnetic anisotropy of neighboring halogen atoms X and Y. In CClF2-CF2-R, the magnetic anisotropy of the atoms gauche to the terminal group and the steric effect of the terminal group are responsible for the 13C NMR chemical shift of a terminal halogenated methyl group, and the inductive effect of the substituent R mainly determines the 13C NMR chemical shift of the difluoromethylene group.

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