Supramolecular amide and thioamide synthons in hydrogen bonding patterns of N-aryl-furamides and N-aryl-thiofuramides

The supramolecular synthon of amide group in the primary and secondary amides is well recognized to be infinite chains of the C(4) type formed by the intermolecular hydrogen bond of the type N–HO=C. On the other hand, there is a lack of structural data for the thioamides. Three compounds belonging to the class of N-aryl-fura-mides (N-(4-bromophenyl)-5-bromo-2-furancarboxamide, N-(4-chlorophenyl)-5-bromo-2-furancarboxamide) and to the class of N-aryl-thiofuramide (N-(4-methoxyphenyl)-2-furanthiocarboxamide) are prepared and characterized by the NMR spectroscopy in solution; molecular and crystal structures in the solid state have been determined by X-ray single crystal diffractometry and the structures in the gas phase by DFT and AM1 calculations. The investigation is carried out in order to establish supramolecular amide and thioamide synthons of hydrogen bonding patterns in these crystal structures. The geometry of the N–HO=C and the N–HS=C type of hydrogen bonds are compared due to the possibility of the N–H amide group to form intramolecular hydrogen bond with the furan oxygen atom, thus, commonly, leading to the three-center hydrogen bond pattern. The competition between the S=C proton acceptor of thioamides and the other proton acceptors (such as methoxy group) for the amide N–H proton donor group has been investigated. In that context, the above-mentioned compounds are correlated with the others of this class, structurally determined, so far.