Journal of the Chemical Society. Perkin transactions II p. 1045 - 1052 (1988)
Update date:2022-08-05
Topics:
Tinant, Bernard
Wu, Shan
Declercq, Jean-Paul
Meerssche, Maurice Van
Masamba, Wayiza
et al.
Five new captodative (cd) substituted cyclopropanes have been synthesized and their structures determined from X-ray diffraction data.These are cis-1,2-dicyano-1,2-dimethyl- (1), trans-1,2-dicyano-1,2-bisethoxycarbonyl- (2), cis-1,2-dicyano-1,2-dimethoxy- (3), trans-1,2-dicyano-1,2-bismethylthio- (4), and trans-1,2-dicyano-1,2-bis(dimethylamino)-cyclopropane (5).These structures have been solved by direct methods and refined by least-squares using 865, 1332, 766, 1075, and 1341 reflections respectively, to R 0.062, 0.041, 0.044, 0.031, and 0.049.This work completes former results and permits the discussion of the influence of polar substituents on cyclopropane geometry in relation to their reported ease of cis-trans isomerization.The effect on ring bond lengths is small but significant: in both captodative and dicapto-substitution, the distal ring bond is shortened and vicinal bonds are lengthened.Mean distal-bond shortenings are proposed for SR, OR, and NR2; the values calculated for C<*>N, C=O, and phenyl agree with published data.The particular facile isomerization of cd cyclopropanes appears best explained, not as the consequence of a destabilized ground state but but rather as increased spin delocalization in the transition state.
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