M. J. Bennett, J. Purdham
May 15, 1978
Citations
0
Influential Citations
2
Citations
Journal
Canadian Journal of Chemistry
Abstract
1,2,4,5-Tetraphenyl-3,6-dicarbomethoxycyclohexa-1,4-diene crystallizes in the monoclinic space group I2/a (a non-standard setting of C2/c) with a = 20.052(2), b = 5.756(1), c = 22.782(2) A, β = 95.73(1)°, and Z = 4. 1,2-Dicarbomethoxy-4,5-dimethylcyclohexa-1,4-diene crystallizes in the orthorhombic space group Pbca with a = 25.627(2), b = 11.240(1), c = 8.342(1) A, and Z = 8. Both structures were solved by direct methods and refined by full matrix least-squares techniques to R = 0.040 and R = 0.036, respectively. Carbon–carbon double bond lengths are similar in the two compounds (1.326 and 1.333 A, respectively), but the single bond lengths are significantly longer in l,2,4,5-tetraphenyl-3,6-dicarbomethoxycyclohexa-1,4-diene (1.518 A) compared with the 1.493 A average found in 1,2-dicarbomethoxy-4,5-dimethyl- cyclohexa-1,4-diene. This and the fact that there are also small deviations from planarity in the former compound are thought to be due to the presence of substituents on the methylenic carbon atoms.