The Chloronium Cation [(C2H3)2Cl+] and Unsaturated C4-Carbocations with C=C and C≡C Bonds in Their Solid Salts and in Solutions: An H1/C13 NMR and Infrared Spectroscopic Study

• Published in: International journal of molecular sciences 2022-08, Vol.23 (16), p.9111
• Main Authors: Stoyanov, Evgenii S., Stoyanova, Irina V.
• Format: Article
• Language: English
• Subjects: Cations; chloronium cation; Decomposition; Density distribution; Electron density; Infrared spectra; Infrared spectroscopy; Isomers; magic-angle spinning NMR measurements; NMR; Nuclear magnetic resonance; Salts; Spectrum analysis; Temperature; Thermal stability; vinyl and propargyl carbocations
• ISSN: 1422-0067; 1661-6596; 1422-0067
• DOI: 10.3390/ijms23169111

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.