The structures of 1,1-dichloro-2,2-diphenylcyclopropane and 1,1-dibromo-2,2-diphenylcyclopropane have been determined from three-dimensional X-ray data collected by counter techniques. The compounds are isomorphous, crystallizing in the monoclinic space group C2h5-P21/c with four molecules per cell. Cell constants for the chloro derivative are a = 6.170 (2), b = 13.673 (4), c = 15.513 (4) Å; and β = 92.24 (2)°; cell constants for the bromo compound are a = 6.246 (2), b = 13.822 (4), c = 15.640 (4) Å; and ß = 93.88 (2)°. The structures have been refined by full-matrix least-squares procedures to conventional R indices of 0.034 (on F) and 0.046 (on F1) for the chloro compound and 0.035 (on F) and 0.067 (on F2) for the bromo derivative. Both structures have unsymmetrical cyclopropane rings with C-C bond lengths of 1.490 (3), 1.520 (3), and 1.529 (3) Å in the chloro compound and 1.477 (6) and 1.508 (6), and 1.509 (6) Å in the bromo compound. The longer bonds in the chloro compound may result from withdrawal of electrons from the cyclopropane ring as a whole. In each structure the shortest C-C bond is that across the ring from the point of phenyl substitution. For other cyclopropanes, this shortening has been observed previously across from substituents which can interact through π orbitals and has been explained by simple molecular orbital arguments. Such simple arguments do not explain the shortenings observed for the compounds studied here since the orientations of the phenyl rings do not allow overlap of the appropriate orbitals.
ASJC Scopus subject areas
- Colloid and Surface Chemistry