Atropisomerism in bi-1,2,3-triazoles: Detection by 1H NMR using chiral shift reagents and torsional barriers calculations

Abstract

The effect of europium tris 3-(heptafluoropropylhydroxymethylene)-(+)-camphorate on the hydrogen signal chemical shift of a series of bi-1,2,3-triazoles was studied by 1H NMR, displaying a signal discrimination which indicates the formation of atropisomers in these molecules. In addition, the rotational barrier around the C5−C5’ bond for bi-1,2,3-triazoles was calculated using the DFT (B3LYP) method with 6-31G** basis set, revealing significant energy barriers (up 34 kcal/mol) at 204–206° dihedral angles and a low atropisomer interconversion. These elements allow a direct method for recognition of chiral bi-1,2,3-triazoles derived from copper-catalyzed azide-alkyne cycloaddition.