The Substituent Effects in Thiophene Compounds. I. 1H NMR and IR Studies in Methyl (Substituted 2-Thiophenecarboxylate)s

The 1H NMR spectra and the IR carbonyl stretching frequencies of methyl (3-, 4-, and 5-substituted 2-thiophenecarboxylate)s have been reported. Good linear correlations between the chemical shifts of the ring protons in methyl (4- and 5-substituted 2-thiophenecarboxylate)s and those of the corresponding protons in substituted thiophenes were observed. The coupling constants in methyl (substituted 2-thiophenecarboxylate)s gave good correlations against the corresponding ones in substituted thiophenes. The IR carbonyl stretching frequencies in methyl (5-substituted 2-thiophenecarboxylate)s were correlated reasonably well with the chemical shifts of 5-protons in 2-substituted thiophenes. The coupling constants in methyl 2-thiophenecarboxylate series were found to vary linearly with the electronegativities of the substituents.