Isotope shift in the proton magnetic resonance of deuterated methanes

The isotope shift in the proton magnetic resonance of deuteromethanes has been examined. By the use of Pople's formula for the chemical shift, it has been shown that the effect is due to vibronic coupling from the bending modes S₄. The chemical shift was evaluated under the assumption that the hydrogen population is linearly dependent on the 2S character of the bonded carbon hybrid. Satisfactory agreement between theoretical and experimental results was obtained.