Double bond pyramidalization in bicyclic alkanes. Ab initio mo calculations on bicyclo[2.2.1] hept-2-ene, bicyclo[2.2.1] hex-2-ene and bicyclo[3.2.1] oct-6-ene derivatives

Abstract

Ab initio STO 3G minimized geometries of bicyclo[2.2.1] hept-2-ene derivatives 9—25, 7-azabicyclo[2.2.1]heptane derivatives 26-29, tetracyclo[4.3 .0.0 2,4.0 3,7]non-8-ene ( 30), tricyclo[4.2.1.0 3,7]non-4-ene ( 31), 2,3-dimethylidene- ( 32) and 2-methylidenebicyclo[2.2.1]heptane ( 33), bicyclo[2.1.1]hex-2-ene ( 34) and tetracyclo[5.1.1.1 3,5.0 2,6]- dec-2(6)-ene ( 35) were obtained. The pyramidalization of the bicyclo[2.2.1]hept-2-ene endocyclic double bond depends upon the nature of the ethano and methano bridges. This is discussed in terms of Houk's torsional effects and Bartlett's repulsion effects. Exocyclic s-cis-butadiene moieties grafted onto bicyclo[2.2.1]heptane skeletons are essentially planar. The bicyclo[2.1.1]hex-2-ene derivatives 34 and 35 are calculated to be planar alkenes, thus suggesting that olefin cis-strainlo[2.2.1]hept-2-enes is not responsible for the pyramidalization of these alkenes.