Polynuclear Magnetic Resonance of Substituted Thiobenzanilides and Benzanilides: Transmission of Substituent Effects through the Thiocarboxamide Group

The 1H, 13C and 19F NMR spectra of 3′- and 4′-substituted 3- and 4-fluorobenzanilides and thiobenzanilides are reported. According to the 19F substituent-induced shifts (SCS), transmission of substituent effects through the NHCS group is less efficient than that through NHCO groups. On the other hand, in thioanilides a greater part of the substituent effect remains on the functional group itself, as follows mainly from 13C SCS of the central carbon. An explanation is possible in terms of the greater polarizability of sulfur, which accommodates charge better than oxygen. Comparison with the isomers studied previously reveals that transmission depends slightly on the direction. It is more efficient through the NHCX group than through the CXNH group: the nitrogen atom as donor interacts more strongly than carbonyl with the substituent effects of acceptor groups.