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Oxatriquinanes are fused, tricyclic oxonium ions that are known to have exceptional stability compared to simple alkyl oxonium salts. C-O bonds in ethers are generally ???1.43???? in length, but oxatriquinane has been found to have C-O bond lengths of 1.54????. A search of the Cambridge Structural Database turned up no bona fide C-O bond length exceeding this value. Computational modelling of oxatriquinane alongside other alkyl oxonium ions indicated that the electronic consequences of molecular strain were primarily responsible for the observed bond elongation. We also show that substitution of the oxatriquinane ring system with alkyl groups of increasing steric demand pushes the C-O bond to unheard of distances, culminating in a tert-butyl derivative at a predicted 1.60????. Chemical synthesis and an X-ray crystallographic study of these compounds validated the results of the modelling work and, finally, an extraordinary 1.622???? C-O bond was observed in 1,4,7-tri-tert-butyloxatriquinane.

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Gunbas, G.; Hafezi, N.; Sheppard, W. L.; Olmstead, M. M.; Stoyanova, I. V.; Tham, F. S.; Meyer, M. P.; Mascal, M. Nat. Chem. 2012, 4, 1018Contributed by Steven Bachrach.Reposted from Computational Organic Chemistry with permissionI have written a number of...
I have written a number of posts discussing long C-C bonds (here and here). What about very long bonds between carbon and a heteroatom? Well, Mascal and co-workers1 have computed the structures of some oxonium cations that express some very long C-O bonds....
C–O bond stretched to record length | Chemistry World - Chemists in the US have stretched the C–O bond to a record length, an ‘extraordinary’ 1.622Å, compared with a typical length of around 1.43Å in ethers. The work not...