Experimental and theoretical study of substituent effect on C-13 NMR chemical shifts of 5-arylidene-2,4-thiazolidinediones

Abstract

The electronic structure of 5-arylidene-2,4-thiazolidinediones has been studied by using experimental and theoretical methodology. The theoretical calculations of the investigated 5-arylidene-2,4-thiazolidinediones have been performed by the use of quantum chemical methods. The calculated C-13 NMR chemical shifts and NBO atomic charges provide an insight into the influence of such a structure on the transmission of electronic substituent effects. Linear free energy relationships (LFERs) have been further applied to their C-13 NMR chemical shifts. The correlation analyses for the substituent-induced chemical shifts (SCS) have been performed with sigma using SSP (single substituent parameter), field (sigma(F)) and resonance (sigma(R)) parameters using DSP (dual substituent parameter), as well as the Yukawa-Tsuno model. The presented correlations account satisfactorily for the polar and resonance substituent effects operative at C-beta. and C-7 carbons, while reverse substituent effect was found for C-alpha. The comparison of correlation results for the investigated molecules with those obtained for seven structurally related styrene series has indicated that specific cross-interaction of phenyl substituent and groups attached at C-alpha carbon causes increased sensitivity of SCS C-beta to the resonance effect with increasing of electron-accepting capabilities of the group present at C-beta.