title: Extreme oxatriquinanes and a record C-O bond length.
abstract: 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 Å in length, but oxatriquinane has been found to have C-O bond lengths of 1.54 Å. 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 Å. Chemical synthesis and an X-ray crystallographic study of these compounds validated the results of the modelling work and, finally, an extraordinary 1.622 Å C-O bond was observed in 1,4,7-tri-tert-butyloxatriquinane.
authors.affiliation: Department of Chemistry, University of California Davis, 1 Shields Avenue, Davis, California                 95616, USA.
authors.forename: Gorkem
authors.initials: G
authors.lastname: Gunbas
authors.forename: Nema
authors.initials: N
authors.lastname: Hafezi
authors.forename: William L
authors.initials: WL
authors.lastname: Sheppard
authors.forename: Marilyn M
authors.initials: MM
authors.lastname: Olmstead
authors.forename: Irini V
authors.initials: IV
authors.lastname: Stoyanova
authors.forename: Fook S
authors.initials: FS
authors.lastname: Tham
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Meyer
authors.forename: Mark
authors.initials: M
authors.lastname: Mascal
mesh_terms: D002244:Carbon / Q000737:chemistry*; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D004986:Ether / Q000737:chemistry; D006575:Heterocyclic Compounds, 3-Ring / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D009861:Onium Compounds / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry*
chemical_list: D006575:Heterocyclic Compounds, 3-Ring; D009861:Onium Compounds; D004986:Ether; D002244:Carbon; D010100:Oxygen