Manifestations of the Alder—Rickert Reaction in the Structures of Bicyclo[2.2.2]octadiene and Bicyclo[2.2.2]octene Derivatives

摘要

The Alder—Rickert ethylene extrusion reaction manifests in the ground state structures of compounds 9—12 which contain the bicyclo[2.2.2]octadiene moiety and compounds 13,14, and 17—20 which contain the bicyclo[2.2.2]octene moiety. A significant decrease of the ~(13)C—~(13)C one-bond coupling constants for the C—C bonds, which break in this fragmentation reaction, suggests lengthening, and hence weakening of these bonds. In the unsymmetrical systems these effects are also shown to be associated with strengthening of the CH_2—CH_2 bond, which is ultimately lost from the molecule as ethylene. Low-temperature crystal structures of compounds 9—12 and 16 provide evidence for similar crystal packing requirements of the CH_2—CH_2 and CH=CH moieties.