CALCULATED AND MEASURED C-13 NMR CHEMICAL-SHIFTS OF THE 2,4,6-TRICHLOROHEPTANES AND THEIR IMPLICATIONS FOR THE C-13 NMR-SPECTRA OF POLYVINYL-CHLORIDE)

13C NMR chemical shifts are measured for each of the carbon atoms in the three stereoisomers of 2, 4, 6-trichloroheptane (TCH). Spectra are recorded from solutions employing a broad range of solvents, as well as the neat liquids, over the temperature range of 25-140°C. The differences in chemical shifts observed between the carbon atoms of the three TCH isomers are virtually independent of solvent for the methine carbons, only slightly solvent dependent for the methyl carbons, and extremely sensitive to solvent for the methylene carbons. The 13C chemical shifts observed for TCH can be predicted, with the exception of those of the solvent-sensitive methylene carbons, by quantitatively calculating the number of three-bond gauche or γ interactions between carbon atoms and between carbon and chlorine atoms. The following γ effects are required to achieve this agreement: γCH2 or CH3, CH = -2.5 ppm, γCH, CH2 or CH3 = -5.0 ppm, and γCH, Cl = -3-0 ppm, where γa, b is the upfield shift observed at carbon a due to atom b, which is γ to a and in the gauche conformation. In addition to the 13C chemical shifts of TCH and their temperature dependence, these γ effects correctly predict the chemical shift differences observed for the methyl and methine carbons between the meso and racemic isomers of 2, 4-dichloropentane and the chemical shift pattern of the methine region in the 13C NMR spectra of poly (vinyl chloride). © 1979, American Chemical Society. All rights reserved.