Analysis of H-1 and C-13{H-1} NMR spectral parameters and geometries of three isomeric diphenylbicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic anhydrides

Diels-Alder adducts of 1,4-diphenyl-1,3-cyclopentadiene and maleic anhydrid e were investigated by recording the H-1 and C-13(H-1) NMR spectra of three isomeric diphenylbicyclo[2.2.1]hept-5-ene endo and exo 2,3-dianhydrides. T he spectra were recorded in CD2Cl2 and analysed completely The effect of th e endo and exo configuration of the anhydride ring on the chemical shifts o f the bridgehead phenyl protons is discussed. The ortho protons of the exo isomers resonate at higher field than those of the endo isomer, and the res onance pattern of the aromatic protons is narrower in the exo than the endo anhydride. The aromatic regions of the spectra are compared with the same regions of the H-1 NMR spectra of the earlier investigated addition product s of 1,4-di-p-tolyl-1,3-cyclopentadiene and 1-phenyl-4-p-tolyl-1,3-cyclopen tadiene with maleic anhydride. Chemical shifts of the bridge protons are ex plained on the basis of X-ray data of the compounds and MacroModel calculat ions on the minimum energy conformations.