Carbon-13 n.m.r. and CNDO/S study of 1,2-indandione and heterocyclic analogues

¹³C n.m.r. spectra are reported for 1,2-indandione, coumarandione and thionaphthenequinone in CDCl₃ solution and for isatin in dimethyl sulphoxide solution. The chemical shifts are assigned and discussed in connection with the influence of the heteroatom on the dicarbonyl group and the aromatic ring. The ¹³C shieldings have also been calculated by means of Pople's perturbation theory using CNDO/S wave functions.