Chlorodicyclopentadienyloxoniobium(V) complexes revisited: the origin of the asymmetry in the 1H- and 13C-NMR spectra, X-ray crystal structures and ab initio/HF and DFT/B3LYP calculations
The 1H and 13C NMR spectra of several 2,6-diheteroarylvinyl heterocycles containing 4-azulenyl moiety were recorded and their proton and carbon chemical shifts were compared with those of the compounds without double bond between the heterocycles. The influence of the nature of central and side heterocycles, molecule polarization and anisotropic effects were revealed. The highest chemical shifts were recorded for the pyrylium salts and the lowest at pyridines, but in the case of the pyridinium salts, the protons chemical shifts at the central heterocycle are more shielded due to a peculiar anisotropy of the attached vinyl groups.
The ground and ionic states of cyclohepta-1,3,5-triene and their relationship to norcaradiene states: New 1H and 13C NMR spectra and analysis of a new experimental photoelectron spectrum by ab initio methods
