Norbornanes. Part 21. Bridging Strain in Norbornyl and Oxanorbornyl Cations

Article abstract of DOI:10.1002/hlca.19880710512

Further evidence is presented that the 2-norbonyl cation is stabilized primarily by C(2)-C(6) bridging, and that C(2)-C(7) bridging leads to prohibitive strain.Thus, a comparison of the heats of hydrogenation of nortricyclene 17 and bicyclo<3.2.0.0^2,7>heptane 18 indicates that the strain energy of the latter is ca. 21.5 kcal/mol higher than that of 17.Furthermore, 6-exo-2-oxabicyclo<2.2.1>heptyl sulfonates 8 ionize with strong O(2) participation to the bridged oxonium ion 12.In contrast, 2-endo-7-oxabicyclo<2.2.1>heptyl sulfonates 11 ionize without O(7) participation to form the unbridged carbenium ion 15.