MOLECULAR-GEOMETRY AND CIRCULAR-DICHROISM SPECTRA OF BICYCLO[2.2.1]HEPTANE-2,3-DICARBOXYLIC ANHYDRIDES AND IMIDES

Several tricyclic anhydrides and imides derived from optically active bicyclo[2.2.1]heptane-2,3-dicarboxylic acids were synthesized, and the ir circular dichroism spectra are reported. On the basis of MNDO calcu lations it was estalished that despite rigidity of the norbornane syst em the five-membered rings of succinic anhydride and imide moieties ar e slightly twisted. The chromophores are flexible and can be more or l ess skewed depending on solvent polarity. The chromophore nonplanarity significantly influences magnitude and sign of the first Cotton effec t associated with the lowest energy n-pi electronic transition. The s ign of the second n-pi Cotton effect is governed by vicinal effect of substituents. The crystal structures of three N-(S)-1-phenylethylimid es were solved to establish the configuration at C-2 of the imide moie ties.