Deuterium isotope effects on aromatic carbon-13 chemical shifts. II. Dependence of one- and two-bond isotope shifts on electron densities of substituted benzenes.

One- and two-bond deuterium isotope effects (1Δ and 2Δ) on 13C chemical shifts of substituted benzenes are reported. The one-bond effects are correlated with the π-electron densities on the observed carbons, and the two-bond effects are correlated with the σ-electron densities on the observed carbons. There are no correlations between 1Δ and 2Δ. 1Δs reflect the direct change on going from a C–H bond to a C–D bond, but 2Δs reflect their indirect effect.