Experimental and NMR theoretical methodology applied to geometric analysis of the bioactive clerodane trans-dehydrocrotonin

trans-Dehydrocrotonin (t-DCTN) a bioactive 19-nor-diterpenoid clerodane type isolated from Croton cajucara Benth, is one of the most investigated clerodane in the current literature. In this work, a new approach joining X-ray diffraction data, nuclear magnetic resonance (NMR) data and theoretical calculations was applied to the thorough characterization of t-DCTN. For that, the geometry of t-DCTN was reevaluated by X-ray diffraction as well as ¹H and 13C NMR data, whose geometrical parameters where compared to those obtained from B3LYP/6-311G++(d,p) level of theory. From the evaluation of both calculated and experimental values of ¹H and 13C NMR chemical shifts and spin-spin coupling constants, it was found very good correlations between theoretical and experimental magnetic properties of t-DCTN. Additionally, the delocalization indexes between hydrogen atoms correlated accurately with theoretical and experimental spin-spin coupling constants. An additional topological analysis from quantum theory of atoms in molecules (QTAIM) showed intramolecular interactions for t-DCTN.