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

Abstract

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.

Spontaneous Transition of Alkyl Carbocations to Unsaturated Vinyl-Type Carbocations in Organic Solutions

“…This procedure eliminated the self-association. The NMR spectrum after a long scan showed a detailed hyperfine structure, which allowed for a confident interpretation [25]).…”

Substitution of H Atoms in Unsaturated (Vinyl-Type) Carbocations by Cl or O Atoms

“…Using divinylchloronium salt (CH 2 =CH) 2 Cl + {Cl 11 − } (preparation is given in [ 13 ]), another similar cation was obtained. A saturated solution of this salt in C 6 HF 5 was kept over hexane vapor, and, after 2 weeks, small crystals appeared.…”

“…Interaction of cations with surrounding anions with the formation of contact ion pairs or the introduction of Cl substituents also contributes to better scattering of the positive charge and its decrease in C=C bonds. The use of carborane superacids has made it possible to obtain and study solid salts of unstabilized vinyl and acetylene carbocations, which are stable at room and elevated temperatures [ 10 , 11 , 12 , 13 ].…”

A new type of C+⋯Hδ−(C=) bond in adducts of vinyl carbocations with alkenes

“…Nevertheless, solid salts of vinyl cations C 3 H 5 + and C 4 H 7 + with carborane anions CHB 11 Cl 11 − were recently obtained, and the structure of the cations was determined by X–ray diffraction analysis 15 – 17 . Salts of methyl-propargyl cation C 4 H 5 + and chlorinated vinyl cations were also obtained, and their structure was determined by NMR 18 , X-ray, and IR spectroscopy 17 , 19 . It turned out that salts of vinyl cations with carborane counterions are stable at least up to 150 °C 15 – 18 .…”

“…Salts of methyl-propargyl cation C 4 H 5 + and chlorinated vinyl cations were also obtained, and their structure was determined by NMR 18 , X-ray, and IR spectroscopy 17 , 19 . It turned out that salts of vinyl cations with carborane counterions are stable at least up to 150 °C 15 – 18 . In solutions in common organochlorine solvents, they appear to be stabler than salts of alkyl carbocations and can be stored for a long time without decomposition under ambient conditions 20 .…”