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

Cyclobutaarenes are highly strained compounds which exhibit unusual geometric features. Introduction of diphenyl substituents on the peripheral C atoms of the cyclobutene ring adds stereoelectronic effects and causes further distortion of the ring structure. The interatomic distances observed for the peripheral C-C bonds in the cyclobutene moiety of the two compounds are in the range 1.71-1.72Å, among the longest of C_sp³-C_sp³ bonds previously reported for similar compounds. The core structure of the phenanthrodicyclobutene derivative is severely twisted due to non-bonding interactions between the chlorine substituents.

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