An analysis of substituent effects on 1H and 13C NMR parameters of substituted furans. Linear free energy relationships and PM3 semiempirical calculations

Forty five furans have been obtained in a synthetic project designed to evaluate monothiosubstituted furans as potential food flavourings. A full NMR (1H and 13C) study and PM3 molecular orbital semiempirical calculations have been carried out. Substituent-induced chemical shifts (SCS) for six and nine substituents at the 2- and 3-positions have been calculated and a separation of inductive and resonance effects of these substituents has been proposed. Finally, a linear correlation between the net atomic charges localized at ring carbons and their 13C NMR chemical shifts has been established.