13C NMR Spectra of Substituted 2-Thiophenecarboxylic Acid Methyl Esters and MNDO Calculations

The 13C NMR spectra have been reported on substituted 2-thiophenecarboxylic acid methyl esters. The chemical shift of ring carbons in methyl (4- and 5-substituted 2-thiophenecarboxylate)s was correlated linearly with that of the corresponding carbons in substituted thiophenes. Plots of the 13C–H coupling constants of methyl (substituted 2-thiophenecarboxylate)s against those of substituted thiophenes showed a good linear relation. The 13C NMR data were interpreted by the stable conformation and percent s character of C–H bonds obtained by MNDO calculation.