Crystal and molecular structure of 1,4-diphenyl-2,3-dioxabicyclo[2,2,1] heptane, C₁₇H₁₆O₂

The crystal structure of 1,4-diphenyl-2,3-dioxabicyclo [2,2,1] heptane has been determined from three-dimensional counter data and refined by full-matrix least-squares procedures. This endoperoxide compound crystallizes from ethanol in space group P2₁/c with cell constants a = 11.797(1), b = 9.051(8), c = 12.472(1) Å, β = 93.78(1) °, Z = 4, D_x = 1.261, and D_m = 1.274 g cm^-3. The final residual for 2238 observed reflections is 0.063. The molecular structure possesses both an unusually long peroxide bond, 1.501(2) Å, and adjoining C-O bonds, 1.459(2) Å. This observation confirms a previously made conjecture that the forced cis coplanarity of the C-O-O-C torsion angle would permit repulsive antisymmetric vicinal orbital interactions between the oxygen centers, destabilizing the peroxide bond relative to that normally encountered as the commonly observed gauche conformation.