The Effect of Fusion of Angular Strained Rings on Benzene: Crystal Structures of 1,2‐Dihydrocyclobuta[a]cyclopropa[c]‐, 1,2,3,4‐Tetrahydrodicyclobuta[a,c]‐, 1,2,3,4‐Tetrahydrodicyclobuta[a,c]cyclopropa[e]‐, and 1,2,3,4,5,6‐Hexahydrotricyclobuta[a,c,e]benzene

Abstract

Noticeable deformations of the benzene framework caused by annelation with strained rings are observed in the crystallographic studies on 1–4. These are the most strained benzene derivatives yet known. The angles at the sp2 carbon atoms in 1 and 3 indicated by an arrowhead are the largest known: 176.9 and 174.9°, respectively. Molecules 2 and 4 display a slight bond length alternation in the arene moiety (0.010–0.023 Å).

Angular Group Induced BondAlternation (AGIBA). A New Face of Substituent Effect Detectedin Molecular Geometry

“…64,81 The increase of bond lengths alternation is mostly interpreted in terms of the variation in hybridisation at the substituted carbon atom, 57,60,78-80 hence it is in line with the SIBL-model. 64,81 The increase of bond lengths alternation is mostly interpreted in terms of the variation in hybridisation at the substituted carbon atom, 57,60,78-80 hence it is in line with the SIBL-model.…”

Extremely Long C—C Bonds in Strained 1,1,2,2-Tetraphenylcyclobutaarenes: 3,8-Dichloro-1,1,2,2-tetraphenylcyclobuta[b]naphthalene, C36H24Cl2, and 3,6,9,10-Tetrachloro-4,5-dimethyl-1,1,2,2,7,7,8,8-octaphenyldicyclobuta[b,h]phenanthrene Toluene Solvate, C68H46Cl4.1.5C7H8

“…This has been demonstrated by crystal structure analyses of two 1,1,2,2-tetraphenylethane-1,2- C---C bond length of 1.54 A, (Toda, Tanaka, Wang & Lee, 1986;Bourne, Nassimbeni &Toda, 1991). Angular strain in the cyclobutaarene fragment also contributes at least 0.04 A to the elongation of the saturated C--C bond (see above; Boese et al, 1994). The unique stereochemistry of these species thus accounts for a C--C stretching of ca 0.1 A.…”

“…The cyclobutene structure observed in this study is characterized by Cw3---Csp3 bond distances in the range 1.710(5)-1.724(5)A and Cw3--Csp2 ° bond distances varying from 1.526(4) to 1.538(4)A. These values have not been corrected for thermal motion effects and do not account for the presence of 'bent bonds' in the four-membered ring (Boese et al, 1994). In the planar naphthocyclobutene compound, the cyclobutene fusion bond has a normal length of 1.409 (4)A, while the adjacent bonds in the benzene ring are considerably shortened [1.351 (5) and 1.360 (4)A].…”

“…A series of low-temperature crystallographic studies of arenes containing fused strained cyclobutene and cyclopropene rings, characterizing the effect of the angular strain on the electronic structure of benzene, have recently been published (Boese & B1/iser, 1988;Bl~iser et al, 1989;Boese et al, 1994). For the benzocyclobutene species, the interatomic dimensions of the four-membered tings were typically found to be near Csp2---Csp2 ° -~ 1.34, "-1.52 and Cw3--Cw3 = 1.58 A.…”

Molecular Shape and Crystal Packing: a Study of C12H12 Isomers, Real and Imaginary

“…For SUKXEB, any attempt at prediction would have been doomed to failure, because the space group of the experimental structure is not one of the most frequent in organic crystals and is not considered in our procedure. For HAYYAH and DMNPTL, the calculated structure with the lowest lattice energy corresponds to the experimental crystal structure ( [29] and [30], resp. ), so that these examples would rank as successful predictions, according to the present rules of the game, which do not consider kinetic or entropic effects.…”