1.3-Dithienium-and 1.3-Dithiolenium Salts, VI ,13C NMR Spectroscopic Investigations on 2-Substituted 1,3-Dithian-2-ylium Cations. Unusual γ-Effects

Abstract

Abstract The 13C NMR chemical shifts of 19 2-substituted 1,3-dithian-2-ylium-tetrafluorborates 1a-1s are discussed in comparison to known analogous 1,3-dithianes and 2-lithio-1,3-dithianes. The unusual γ-effects (up to 9 ppm), which can also observed in other six-membered ring systems, are explained by the electric field effect (σ-polarisation effect). The electron density distribution can be estimated qualitatively by comparison with the 1,3-dioxan-2-ylium-and cyclohexylcations.