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.

Pressure Induced Topochemical Polymerizationof Solid Acryalmide Facilitated by Anisotropic Response of Hydrogen Bond Network

“…According to our calculations, intermolecular C-C and C-O bonds form at distances of ∼1.46 Å to ∼1.51 Å and ∼1.37 Å during polymerization, which are well below the highest possible C-C and C-O single bond distances (∼1.8 Å and ∼1.6 Å, respectively) as reported in the literature. 87,88 In fact, our calculated critical distances are quite close to the C-C distance of ∼1.43 Å in solid acetylene polymer, reported by Bernasconi et al 4 Although polymerization by the formation of C-C bonds is common, activation of the C-O mode is rare. 89…”

Pressure Induced Topochemical Polymerizationof Solid Acryalmide Facilitated by Anisotropic Response of Hydrogen Bond Network

“…According to our calculations, intermolecular C-C and C-O bonds form at distances of ∼1.46 Å to ∼1.51 Å and ∼1.37 Å during polymerization, which are well below the highest possible C-C and C-O single bond distances (∼1.8 Å and ∼1.6 Å, respectively) as reported in the literature. 81,82 In fact, our calculated critical distances are quite close to the C-C distance of ∼1.43 Å in solid acetylene polymer, reported by Bernasconi et al 1 Although polymerization by the formation of C-C bonds is common, activation of the C-O mode is rare. 83 Since the acrylamide units across the crystal are only weakly interacting, it is possible that there is more than one minimum at a given pressure.…”

Acceleration of Acetal Hydrolysis by Remote Alkoxy Groups: Evidence for Electrostatic Effects on the Formation of Oxocarbenium Ions

“…Electrostatic stabilization of the oxocarbenium ion 17 which forms upon hydrolysis is consistent with the relative rates (Scheme , pathway b) 11. 12 Electrostatic stabilization would require the alkoxy group to be close to the acetal carbon atom,11, 12 but the carbon–oxygen bond distances would be much longer31 than they would be for an oxonium ion 32. As a result, the relative rates of hydrolysis should not track the ring strain closely because a new ring would not be fully formed.…”