Hemispiroalkaplanes: hydrocarbon cage systems with a pyramidal-tetracoordinate carbon atom and remarkable basicity

A new class of saturated hydrocarbons, in which a spiropentane-type unit is bound by a cyclic hydrocarbon, has been investigated by using ab initio molecular orbital calculations at the B3-LYP and MP2 levels. These molecules have been given the trivial name hemispiroalkaplanes. Hemialkaplanes, which are analogous molecules built-up from a neopentane-type unit and a cyclic hydrocarbon, have also been examined. The hemispiroalkaplanes are predicted to contain a pyramidal-tetracoordinate carbon atom that possesses a lone pair of electrons. Protonation at this apical carbon atom is found to be highly favourable, resulting in a remarkably high basicity for a saturated hydrocarbon. The proton affinities of the hemispiroalkaplanes are calculated to be more than 1170 kJmol(-1), even greater than that of the diamine "proton sponges". Structural parameters, heats of formation and strain energies for the novel hydrocarbons are detailed.