A Raman and infrared study of 1-furoyl-3-monosubstituted and 3,3-disubstituted thioureas

Raman and IR spectra of two series of 1-furoylthiourea derivatives (19 compounds) were recorded and compared in order to identify the vibrations, which involve contributions from motions within the thioureido (NCSN) core. This procedure allowed an unequivocal identification of the ?(Cdouble bond; length as m-dashS) vibration in these spectra. In 3-monosubstituted furoylthioureas (Series 2) the carbonyl group and the proton on N3 are engaged in a strong hydrogen bond interaction. This leads to an ?S?-shaped conformation of the Cdouble bond; length as m-dashO and Cdouble bond; length as m-dashS groups where these donor sites reach a maximum separation. In this conformation, the ?(Cdouble bond; length as m-dashO) vibration is not influenced by the substituent. In the absence of that hydrogen bridge, in 3,3-disubstituted thiourea derivatives (Series 1), the Cdouble bond; length as m-dashO and Cdouble bond; length as m-dashS groups adopt an ?U?-shaped conformation. In this conformation, the ?(Cdouble bond; length as m-dashO) vibration shows a pronounced substituent dependence. These thiourea derivatives have been tested as ionophores for heavy-metal ion selective electrodes and their behavior in that sense correlates with the observed Raman and IR absorptions. The best performance in that application corresponds to compounds of Series 2, which showed the highest frequency values of the ?(Cdouble bond; length as m-dashS) vibration. This fact was related to an appropriated nucleophilic character of the sulphur atom. From these data, Raman and IR spectra of these thiourea derivatives could be used as a predictor on their expected behavior in analytical applications as ionophores.