H-BRIDGED ALTERNATIVES TO THE HOMOLOGS OF CYCLOPROPANE

Alternative H-bridged structures (6, 7 and 8) for homologues of cyclop ropane (1) have been calculated using ab initio MO methods at the MP2/ 6-31G and MP/LANL1DZ levels. The energy difference between the classi cal structure 1 and its bridged analogue 6 decreases in going from C t o Pb (1 vs. 6: C 197.0, Si 84.0, Ge 36.0, Sn -1.7, and Pb -45.4 kcal m ol(-1)). Structure 6C is not a minimum, and 6Pb is the lowest energy m inimum that has been located in the present study. The natural bond or bital method was used to understand the nature of bonding in these mol ecules. Strain energies of three membered rings are estimated using Eq . (1). Isolobal analogy connects 6 to B3H9 and (CpCoCO)(3).