ABINITIO SEARCH FOR THE STRUCTURE OF THE 4-PROTOADAMANTYL CATION

The 4-protoadamantyl cation region of the C10H15+ potential energy hypersurface is searched by means of RHF-SCF calculations and the STO-3G, 6-31G, and (in part) 6-31G* basis sets. Two structures are found. The structure with C(s) symmetry is postulated to be the primary intermediate in the solvolysis of 4-endo-protoadamantyl derivatives. It is calculated to be 8 kJ/mol less stable than the second structure which has no symmetry. The asymmetric cation is postulated to be the primary intermediate in the solvolysis of 4-exo-protoadamantyl derivatives. It is 7 kJ/mol less stable than 2-adamantyl cation to which rearrangement is hindered by a very small barrier. Rearrangement of the C(s) structure is expected to be hindered by relatively large barriers. It may be generated directly from bicyclo[4.3.1]dec-3-en-8-yl derivatives. The C(s) cation is characterized by IGLO calculations of C-13 and H-1 NMR chemical shifts.