Conformational rigidity and flexibility of the paracyclophane skeleton in substituted [2.2]paracyclophanes

Abstract

The character of distortions of the paracyclophane skeleton in various substituted [2.2]paracyclophanes was analyzed based on X ray diffraction data. The rigidity of the skeleton is provided by ethylene bridges and flexibility of the benzene rings, which adopt a boat confor mation. The flexibility of the skeleton is manifested in the displacement of the benzene rings with respect to each other and conformational changes of ethylene bridges. The changes in these characteristics are very sensitive to intra and intermolecular steric factors and are indicative of the absence of strong specific stacking interactions between the be nzene rings. Precision X ray diffraction study and quantum chemical calculations for unsubstituted [2.2]paracyclophane and 4,7 benzoquinono[2.2]paracyclophane demonstrated that there are no attractive interactions between the benzene rings, and the electron density is localized predominantly on the outer surface of the rings. This fact can be considered as the "cage molecular" effect of the [2.2]paracyclophane skeleton. Key words: [2.2]paracyclophane, [2.2]paracyclophane derivatives, influence of substitu ents and π-π interactions in the [2.2]paracyclophane skeleton.

Arene Exchange in the Ruthenium–Naphthalene Complex [CpRu(C10H8)]+

“…The mean planes of the arene rings in 2g are almost parallel to each other (1.9°) and are separated by 2.925 Å, which is a bit shorter than that for the paracyclophane (2.994 Å). This shortening is generally attributed to the acceptor effect of metal atom, which decreases the electron density between the aromatic decks and therefore reduces their repulsion 31. The perimeter of the coordinated C 6 ring is 0.152 Å larger than that of the noncoordinated one.…”

Paracyclophanes as Model Compounds for Strongly Interacting π-Systems, Part 3: Influence of the Substitution Pattern on Photoabsorption Properties

“…Such structures have been observed previously only for different pseudo -para -[2.2]paracyclophanes , but not for their constitutional isomers pseudo - gem -, pseudo - ortho -, or pseudo - meta -[2.2]paracyclophanes. The latter molecules all show the D 2 skeleton of PC with twisted −(CH 2 ) 2 − bridges. − …”

Paracyclophanes as model compounds for strongly interacting π-systems. Part 1. Pseudo-ortho-dihydroxy[2.2]paracyclophane

“…The geometry is thus in line with other pseudo-ortho-, pseudo-gem-, or pseudo-meta-[2.2]paracyclophanes, which show throughout the D 2 skeleton with twisted -(CH 2 ) 2 -bridges. [39][40][41] In addition o-DHPC shows another type of geometric distortion: the two aromatic p-systems are tilted with respect to each other giving rise to a structure that is sketched on the right hand side of Fig. 1.…”