Orthogonene redux: a nearly orthogonal alkene predicted to exhibit considerable stability. A computational study.
A strongly twisted, as yet unknown, alkene, orthogonene (tetracyclo[8,2,2,0(2,7),0(3,10)]tetradecene-2(3)), was computationally reinvestigated: earlier work had indicated that the stereoisomer with the pair of bridgehead hydrogens on the methine group at one end of the double bond syn to the pair at the other end (C-H/C-H "up-up/up-up", C(2) symmetry, B3LYP/6-31G double bond angle 83 degrees) is at best of low stability, rearranging with a very small barrier to a carbene or possibly a cyclopropane. Here it is shown that the anti ("up-up/down-down") stereoisomer (ideally D(2) symmetry, CASSCF(4,4)/6-31G* double bond torsional dihedral angle 88 degrees) is much more stable: the barrier to rearrangement to a carbene is calculated to be ca. 200 kJ mol(-1) (CASSCF(4,4)/6-31G*), indicating this compound to be a realistic synthetic objective. The vertical ionization energy of this molecule is predicted to be ca. 5.3 eV, comparable to that of the alkali metals and similar to that predicted by others for a hypothetical planar tetracoordinate carbon molecule.
Lewars
Errol G
EG
Department of Chemistry, Trent University, Peterborough, Ontario, Canada K9J 7B8. elewars@trentu.ca