Experimental and simulated 1H and 13C NMR spectra (GIAO/DFT approach) and molecular and crystal structures of dimethyl-dinitro-azo- and dimethyl-dinitro-hydrazo-pyridines

The 1H and 13C NMR spectra of the 4,4′(or 6,6′)-dimethyl-3,3′-dinitro-2,2′-azo- and hydrazo-pyridine have been measured in the solid state and solution. The spectral data have been analyzed on the basis of DFT quantum chemical calculations using the B3LYP/6-311G, 6-311++G and 6-311G∗∗ approaches. The structures of all molecules have been optimized starting from trans and cis molecular geometry and additionally from diimino form for hydrazoderivatives and compared to the XRD data. The optimization process always led to the trans – isomers. The influence of the azo-bond on the electronic properties of the whole system was analyzed. The role of the hydrogen bond in the structure stabilization of the hydrazo-derivatives has been discussed.

► The 1H and 13C NMR spectra of the 4,4′(or 6,6′)-dimethyl-3,3′-dinitro-2,2′-azo- and hydrazo- pyridine. ► Application of GIAO/DFT procedure for calculation of chemical shift. ► The shielding of 5,5′ - carbons as a result of azo and hydrazo bonds interaction. ► Influence of the N–H···O intramolecular hydrogen bonding on the structure and stabilization of the hydrazo compounds.