Secondary thioamide group deformations in different surroundings: The case of intramolecular N [sbnd]H···N hydrogen bond – An X-ray study combined with theoretical calculations

Abstract

Structures of several β-amino-functionalized secondary thioamides capable to form intramolecular hydrogen bond N H ···N have been determined by X-ray diffraction and ab initio calculations. Both methods show comparable results for the bond lengths and angles, although the N ···N distances is slightly longer in the calculated structures. Particular attention has been directed to the deformations of the thioamide group caused by steric constraints. Out-of-plane deformations of the thioamide group are described in terms of bending (χ C and χ N) and twisting ( τ) parameters. The X-ray and ab initio results show that the thioamide group displays high resistance to steric stress which is in this case caused by intramolecular hydrogen bond and deviations of the thioamide group from planarity are small if any. Some sp 2 bond angles in the thioamide group of the molecules under exploration as well as some tetrahedral bond angles in the saturated parts of the molecules are changed from ideal values in order to retain the thioamide group planarity.