TOWARD AN UNDERSTANDING OF THE CUBYL AND RELATED CAGED CARBOCATIONS

The product ratios observed upon fluorodeiodination of a series of caged cyclobutane-containing iodides are explained on the basis of the relative energies of the intermediate cations involved. The relative energies of these cations have been evaluated by ab initio calculations with the inclusion of electron correlation (MP2/6-31G*//RHF/3-21G; MP2/6-31G**), the results of which lend support to the view that hyperconjugative involvement of the cationic center with the alpha,beta and beta,gamma C-C bonds in each cyclobutyl moiety is the critical factor responsible for the stability of the cation in each case. The degree of stabilization of the cations is a reflection of the number and relative importance of several resonance contributors (corresponding to the involvement of the carbon sigma-framework) to their overall structure and is strongly dependent on the geometry of the rigid carbon framework in each case.