Isotope effects on the 13C NMR chemical shifts of 5‐substituted indoles: Evidence for electron density dependence on the hydrogen (deuterium) atom

Abstract The dependence of the deuterium / hydrogen NMR isotope effects on 13 C chemical shift (DHIECS) values on the electron density at the hydrogen (deuterium) atom in a series of para ‐like substituted indoles with a partially deuterated NH site, measured as 0.83 M solutions in DMSO‐ d 6 , is established on the basis of a series of correlations relating the isotope shifts with Hammett‐type í parameters, 1 H(NH) chemical shifts, 15 N chemical shifts and group electronegativity. The sensitivity of the n Δ isotope effects appears to be connected closely with electron redistribution at the 5‐substituent of the carbon atom under consideration.