A new type of C⋯H(C=) bond in adducts of vinyl carbocations with alkenes.

By X-ray diffraction analysis and IR spectroscopy, it was established here that vinyl carbocations CH/CH with carborane counterion CHBCl form stable monosolvates CH⋅CH/CH⋅CH with molecules of alkenes CH/CH. They contain molecular group =C⋯H-C= with a new type of bond formed by the H atom of the H-C= group of the alkene with the C atom of the C=C group of the carbocation. The short C----C distance, equal to 2.44 Å, is typical of that of X----X in proton disolvates (LH) with an quasi-symmetrical X-H⋯X moiety (where X = O or N) of basic molecule L. The nature of the discovered bond differs from that of the classic H-bond by an distribution of electron density: the electron-excessive H atom from the (=)C-H group of the alkene is attached to the C atom of the carbocation, on which the positive charge is predominantly concentrated. Therefore, it can be called an inverse hydrogen bond.