TOWARD AN UNDERSTANDING OF THE CUBYL AND RELATED CAGED CARBOCATIONS

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