Acta Cryst. (1969). B25, 2465The Structure of 5-Norbornene-2,3-endo-diearboxylie Anhydride
BY RICCARDO DESTRO, GIUSEPPE FILIPPINI, CARLO MARIA GRAMACCIOLI AND MASSIMO SIMONETTA
Istituto di Chimica Fisica, Universitdt di Milano, Milano, Italy (Received 3 February 1969)The crystal and molecular structure of 5-norbornene-2,3-endo-dicarboxylic anhydride* has been determined and refined by least-squares methods. The crystals are orthorhombic, space group P2~212j, with a= 13"539, b=9"565, c=5"972/~ and four molecules per unit cell. Intensity data were collected visually from Weissenberg photographs about two crystal axes. The final R index is 0.071 ; the average standard deviation in the atomic positions is about 0.004 A,. The anisotropic temperature factors of the heavier atoms in the molecule can be accounted for by a Schomaker-Trueblood rigid-body treatment; on this basis, corrections to the observed bond distances are in the range 0"007-0.010/~. In the norbornene nucleus, the bridgehead angle C(1)-C(7)-C(4) is 93.5 °. The geometry of the anhydride group is closely similar to that found in succinic anhydride. The two C-C single bonds which connect the anhydride ring with the cyclopentene ring are found to be significantly longer (1.57 and 1.58/~) than normal. A similar feature observed in cyclopentadiene dimer probably accounts for its chemical reactivity in the Cope rearrangement.