Introduction Conformational research of amide group

For example, variable-temperature 1H, 13C and 15N NMR has been previously successfully used to study hydrogen bond geometries in polar aprotic environment [41] and [42], inter- and intramolecular proton tautomerism [25] and [43], conformational isomerism [44] and [45] and other phenomena. In this work we also start our discussion with the temperature-dependent 1H and 13C NMR spectra of compounds 1, 2 and 3 dissolved in CDCl3, (CD3)2CO, CD3OD or tetrahydrofuran-d8 (THF-d8), presented in Fig. 1 and in Figs.