Electronic absorption and circular dichroism spectra of the perturbed coplanar cis-diene chromophore in deuterium- and methyl-substituted 7,7-dimethylbicyclo(4. 1. 1)octa-2,4-dienes

The optically active monodeuterated 7,7-dimethylbicyclo(4.1.1)octa-2,4-dienes have been prepared with known absolute configuration from (+)-nopinone. Access to their methyl congeners has been achieved from (+)-..cap alpha..-pinene and (+)-nopinone, respectively. The chirality is due solely to isotopic substitution. The contributions of the C-D and C-CH/sub 3/ groups to the observed absorption and circular dichroism spectra are analyzed. In particular, attention is directed to the planar cis-1,3-diene unit, the resultant zero dihedral angle between the C/sub 2/-C/sub 3/ and C/sub 4/-C/sub 5/ bonds at equilibrium, and the consequences of this unique fixed geometry.