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

Abstract

Introduction of Cl and O atoms into C4-vinyl carbocations was studied by X-ray diffraction analysis and IR spectroscopy. Chlorine atoms are weak electron acceptors in ordinary molecules but, within vinyl carbocations, manifest themselves as strong electron donors that accept a positive charge. The attachment of a Cl atom directly to a C=C bond leads to an increase in the e-density on it, exceeding that of the common double bond. The positive charge should be concentrated on the Cl atom, and weak δ− may appear on the C=C bond. More distant attachment of the Cl atom, e.g., to a C atom adjacent to the C=C bond, has a weaker effect on it. If two Cl atoms are attached to the Cγ atom of the vinyl cation, as in Cl2CγCδHCαHCH3, then the cation switches to the allyl type with two practically equivalent and almost uncharged CγCδCα bonds. When such a strong nucleophile as the O atom is introduced into the carbocation, a protonated ester molecule with a C–O(H+)–C group and a C=C bond forms. Nonetheless, in the future, there is still a possibility of obtaining carbocations with a non-protonated C–O–C group.

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 .…”