Hyperconjugation in strained bridgehead cyclobutyl cations: an ab initio study of bicyclo[1.1.1]pent-1-yl cubyl and norcubyl cations

Abstract

Ab initio molecular orbital calculations (MP2/6-31G**) provide strong evidence that the bicyclo[1.1.1]pent-1-yl, cubyl and tricyclo[3.1.1.0^3,6]hept-6-yl (6-norcubyl) cations are principally stabilized by hyperconjugative interaction of the strained α–β and β–γ carbon–carbon bonds with the (vacant) cationic p-orbital; the degree of interaction is strongly dependent on the geometry of the charged four-membered ring in each case.