High resolution NMR spectroscopy of heteroaromatic cations. II—pyrylium, thiapyrylium and seleninium cations

High resolution 1H, proton coupled 13C and broad‐band decoupled 13C{1H} spectra have been recorded for pyrylium, thiapyrylium and seleninium tetrafluoroborates in CD3CN. Analysis of these spectra has provided accurate values and relative signs of all 1H,1H and 13C,1H coupling constants, as well as the magnitudes of all one‐ and three‐bond 13C,13C couplings observable in naturally occurring doubly‐labelled isotopomers. For the seleninium cation, the magnitudes and relative signs of all 77Se,1H and 77Se,13C coupling constants were also obtained. The chemical shifts and coupling data are compared, on a qualitative basis, with existing theoretical predictions.