Additivity of NMR isotope shifts

One of the most interesting and useful aspects of the isotope effect on nuclear magnetic shielding is the proportionality of the shift to the number of substituted atoms in equivalent positions. In this paper we show the quantitative basis for the additivity of isotope shifts in NMR, using the CX/sub 4-n/Y/sub n/ (X,Y = H,D,T) system and the linear triatomic systems CO2, NNO, and OCS as examples. We also predict small deviations from additivity and find that these deviations are consistent with those observed for 14N shifts in the NH/sub 4-n/D+/sub n/ homologous series. Furthermore, we determine the mass dependence of the one-bond isotope shift