C-13 NMR spectra of pyridine chalcone analogs

Abstract

C-13 NMR spectra of two series of pyridine chalcone analogs were determined in deuterated dimethylsulphoxide (DMSO-d(6)). It was established that these compounds were in more stable E-configurations except for the 4-pyridalacetophenone which was in Z-configuration. On the basis of the Hammett correlations of C-13 NMR chemical shifts of the ethylenic bond carbon atoms and the a values for the pyridine "aza" groups, the polarization of ethylenic bonds were discussed. It was established that the opposite effect of the pyridine substituents at the electronic density distribution in pyridalacetophenone and cinnamoylpyridines depends on its direct bonding to the ethylenic carbon or the transmission electronic effects via the carbonyl group, respectively.