1988 Volume 4 Issue 4 Pages 353-355
Carbon-13 NMR spectra of a number of m- and p-substituted benzenesulfonic acids in basic deuterium oxide solutions have been obtained. Simple additivity rules for chemical shifts are totally useless for all carbons except for several carbons in p-CH3, p-Et, and p-Cl derivatives. Deviations of a few ppm have been rationalized for 1, 3- and 1, 4-disubstituted benzenes, but deviations of 7ppm are the largest among C-13NMR chemical shifts data so far reported. The astonishing deviations are observed at the carbon attached to sulfo anion and at both adjacent carbons. The nature of the sulfo group changes according to the second substituent; it is not regulated by the substituent parameters which include various kinds of sigma values.
