A series of 33 ß-nitrostyrenes has been prepared and their 13C N.M.R. spectra have been determined in dimethyl sulphoxide and in deuterochloroform (where soluble). Hammett correlations between substituent and the chemical shift of both the para ring carbons and the a-carbon of the ethenyl group have been shown to be only approximate. In contrast, an excellent correlation has been observed between the chemical shift of the ß-carbon of the ethenyl group and Hammett s+ constants in all cases except those involving para substituents capable of exerting a - R effect. Possible reasons for this are considered. The system appears to be the first reported one where 13C measurements for both meta- and para-substituted compounds give rise to correlations in which agreement lies well inside the limits of experimental error, and shows promise as a convenient method for calculating substituent constants and studying their variation with solvent.