A Correlation between β-Hydrogen Isotope Effects on Carbon-13 NMR Chemical Shifts in Unsaturated Systems and the Strength of Hyperconjugative Interactions

Article abstract of DOI:10.1021/ja00285a006

β-Hydrogen isotope effects on the carbon-13 NMR chemical shifts of the trigonal carbon in CL3C(R)=X (L=H, or D) are reported for 15 substances inwhich the positive charge density at the trigonal carbon is regulated through systematic variation of R and X.A linear relationship is found between these isotope effects and the chemical shifts of the trigonal carbons, and this is taken as evidence for dependence of the magnitude of these isotope effects upon the strength of the hyperconjugative interaction between CL3 and C(R)=X.An explanation of hyperconjugative NMR isotope effecs in terms of anharmonic carbon-hydrogen bond-bending vibrations is advanced.