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The isotope effects of deuterium, manifested in the13C NMR spectra of complexes of deuterated hexamethylbenzenes C6(CD3)n·(CH3)6-n with the nitrosonium cation, have been studied. The small values observed for the isotopic perturbation are evidence of p-bonding of the NO+ group the hexamethylbenzene molecule. The applicability of an additive scheme of calculation of isotope effects for the ring carbon atoms of the complexes, based on the increments of replacement of the CH3 group by CD3 in hexamethylbenzene, has been demonstrated.

Dynamic PMR has been used in a kinetic study of degenerate rearrangement of 5,6-X2-1-H-1, 2-dimethylacenaphthylenonium ions (X=CH3, Br), accomplished by means of a 1,2-shift of the hydrogen atom. It has been found that the free energy of activation of the 1,2-shift of the H atom in the 5,6-X2-1-H-1,2-dimethylacenaphthylenonium cation (X=H, CH3, Br), in the 1-H-1,2-dimethylcyclopentyl cation, and in 5-H-1,2, 3,4,5-pentamethyl-1,3-cyclopentadiene exhibits a linear correlation with parameters characterizing the electron density on the atom to which the migrant is shifted.

1.Acceleration of the degenerate and nondegenerate rearrangement of long-lived 1-R-1,2,3,4,5,6-hexamethylbenzenium ions (R=Me, Ph) on alumina surfaces as compared with solutions has been observed.2.These results contradict the criterion of the involvement of carbocations as intermediates in heterogeneous catalytic processes, which requires that the activation energies of the acid-catalyzed isomerization of hydrocarbons under homogeneous and heterogeneous conditions should be similar.

1.The structure of an episulfonium ion has been determined for the first time, on the basis of 1,2-dimethylacenaphthylene-1,2-S-phenylepisulfonium tetrachloroaluminate as an example; this material exhibits pyramidal configuration about the S atom and a cis distribution of the phenyl and acenaphthene fragments, which are retained in solution. The S+-C1, 2 bond lengths are considerably longer than the S+-C bond lengths normally observed in sulfonium ions.2.The episulfonium ring possesses significant electron withdrawing character.

Conclusions In the example of 1,2-shifts of various migrants (Rm) in 1-Rm-2-hydroxy-1,3,4,5,6-penta-methylbenzenonium ions, it has been demonstrated that a quantitative description can be given for nondegenerate carbocation rearrangements within the framework of an approach that has been formulated previously for degenerate rearrangements of arenonium ions. In the example, of carbocations of the acenaphthene series, it has been established that this approach is also applicable to carbocations of a different structural type.

The rate of the 1,2 hydrogen atom shift in the degenerate rearrangement of 1,2,3,4,5-pentamethyl-1,3-cyclopentadiene is only slightly sensitive to variation in the medium.

The protonation of unsaturated organic compounds is one of the general methods for the generation of carbocations. Strong Brönsted acids in which a hydrogen atom is attached directly to an atom having high electronegativity (O, Hal) are usually employed for this purpose. We found that CH acids can also be used for the generation of carbocations.