1H and 13C NMR spectroscopy of structural isomers of pyridinephosphonic acids

In this work six isomeric pyridinephosphonic acids were investigated. Three of them are mono- and the other three are disubstituted derivatives of pyridine. The compounds dissolved in D2O have been characterized by using the 1H and 13C NMR spectroscopy (both standard and modern techniques such as two-dimensional heterocorrelation measurements, e.g. gHMQC and gHMBC) in order to reveal the differences in their structures. Experimental data were compared with theoretically predicted chemical shifts on the DFT/GIAO level of theory for DFT/B3PW91/6-311++G∗∗ optimized geometries. A quantum-chemical analysis was performed for isolated molecules and more complex systems in order to discuss the type of intermolecular interactions occurring in the conducted experiments. The comparison between experimental and calculate data allowed us to conclude that in the investigated conditions the interaction between molecules of investigated compounds seems to be fundamental, however, the presence of water can not be also neglected.