The Crystal and Molecular Structures of 1,1 -Dibromo-trans-2,3-diphenylcyclopropane and 1,1 -Dibromo-trans-2,3-bis(4'-nitrophenyl)cyclopropane. The Effects of Halogen and Phenyl Substituents on Cyclopropane Geometries

The structures of l, l-dibromo-trans-2,3-diphenylcyclopropane (1) and l, l-dibromo-trans-2, 3-bis(4'-nitrophenyl)-cyclopropane (2) have been determined by conventional x-ray crystallographic techniques. The cell constants for 1 are a = 15.150 (4), b = 7.180 (2), c = 12.405 (5) ¥, and β= 90.87 (1)°; the space group is C2h6-12/c. The cell constants for 2 are a = 15.613 (3), b = 13.623 (2), and c = 7.359 (1) ¥ the space group is D2h-Pnna. The structures of 1 and 2 were refined by full-matrix least-squares techniques to conventional R indices of 0.028 and 0.035, respectively. Both cyclopropanes have crys-tallographically imposed C2 symmetry. The cyclopropane rings in both are symmetrical with average ring bond lengths of 1.516 ¥. No large substituent effects are observable for bromine or phenyl groups. The nitrophenyl-substituted cyclopropane ring exhibits exactly the same geometry as the phenyl-substituted cyclopropane. It is thus apparent that electron withdrawal by phenyl substituents is unimportant. A comparison of these and other known cyclopropane structures is made and a discussion of cyclopropane substituent effects with respect to both molecular orbital and hybridization schemes is presented.