C-13 NUCLEAR-MAGNETIC-RESONANCE STUDY OF THE SUBSTITUENT EFFECTS IN SUBSTITUTED 2-THIOPHENECARBOXANILIDES AND 3-THIOPHENECARBOXANILIDES

H-1- and C-13 NMR spectra of some 2 (2TCA) and 3-thiophenecarboxanilid es (3TCA), metaor para-substituted in the phenyl ring, were recorded i n DMSO-d(6) solutions. The effect exerted by the substituent, X, on th e C chemical shifts of the thiophene as well as the carbamoyl carbon a toms, albeit relatively small, could be interpreted in terms of the Ha mmett equation. The obtained rho value (0.78) for the CO of para-subst ituted 2-thiophenecarboxanilides is positive, which indicates a normal polar effect of X, similar to that previously reported for benzanilid es (rho = 0.86). The rho values obtained for the thiophene carbon atom s, on the other hand, suggest an alternate polarisation on these carbo n atoms in both series of the investigated thiophenecarboxanilides. Th e polar and resonance effects of X on the C-para, CO, C-2, C-3 and C-5 carbon atoms of 2TCA, 3TCA and 5-nitro-3-thiophenecarboxanilides (NTC A) have been analysed by means of a dual substituent parameter (DSP) e quation.