Experimental and theoretical conformational studies of hydrazine derivatives bearing a chromene scaffold

Abstract A conformational study of two novel hydrazine derivatives bearing a chromene moiety was carried out using ab initio and DFT quantum chemical methods, dynamic NMR and IR spectroscopy. The theoretical calculations predict and the experimental NOESY spectra confirm the (E)-anti,anti conformation as the most stable one in solution for the compounds (N'-[(E)-(2-methyl-2H-1-benzopyran-3-yl)methylidene]benzohydrazide and 4-hydroxy-N'-[(E)-(2-methyl-2H-1-benzopyran-3-yl)methylidene]benzohydrazide). The barriers of rotation around the amide bond in the studied compounds, ΔG≠, are in the range of 14.8–15.9 kcal mol−1 and were reproduced very well by the DFT calculations at the SMD/B3LYP/6-31 + G(d,p) level of theory. The GIAO 1H and 13C chemical shifts calculated in DMSO and chloroform are in very good agreement with the experimental NMR data.