Solid salts of the divinyl chloronium (C2H3)2Cl+ cation (I) and unsaturated C4H6Cl+ and C4H7+ carbocations with the highly stable CHB11Hal11− anion (Hal=F, Cl) were obtained for the first time. At 120 °C, the salt of the chloronium cation decomposes, yielding a salt of the C4H5+ cation. This thermally stable (up to 200 °C) carbocation is methyl propargyl, CH≡C-C+-H-CH3 (VI), which, according to quantum chemical calculations, should be energetically much less favorable than other isomers of the C4H7+ cations. Cation VI readily attaches HCl to the formal triple C≡C bond to form the CHCl=CH-C+H-CH3 cation (VII). In infrared spectra of cations I, VI, and VII, frequencies of C=C and C≡C stretches are significantly lower than those predicted by calculations (by 400–500 cm−1). Infrared and 1H/13C magic-angle spinning NMR spectra of solid salts of cations I and VI and high-resolution 1H/13C NMR spectra of VII in solution in SO2ClF were interpreted. On the basis of the spectroscopic data, the charge and electron density distribution in the cations are discussed.
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Stoyanov et al. (2022) studied this question.