ortho-Diethynylbenzene dianion
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| Names | |
|---|---|
| IUPAC name
1,2-Phenylenebis(ethyn-1-ide)
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| Other names
ortho-Diethynylbenzene dianion, o-Diethynylbenzene dianion
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| Properties | |
| C 6H 4C2− 4 | |
| Related compounds | |
Related bases
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Meta-diethynylbenzene dianion |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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The ortho-diethynylbenzene dianion is a superbase with the highest calculated proton affinity of any chemical species observed to date.[1][2] It was first observed in 2016 using mass spectrometry experiments by researchers in Australia.[1] Its calculated proton affinity of 1843.3 kJ/mol places it above previously-known superbases such as the methyl anion (1735.5 kJ/mol)[3] and the lithium monoxide anion (1782 kJ/mol)[4].
Preparation and reactions
A methanolic solution of 3,3'-(1,2-phenylene)dipropiolic acid, made basic with aqueous ammonia to aid the formation of the anion, is first subject to electrospray ionization (ESI). The resulting ions are then isolated in a quadrupole ion trap and subject to collision-induced dissociation (CID) twice. The first isolation/CID cycle isolates the dicarboxylate and induces a single decarboxylation, producing a singly-decarboxylated dianion with a mass-to-charge ratio (m/z) of 82. The second cycle isolates this species and induces a second decarboxylation, producing the title dianion at m/z = 62.[1]
Reactions of the dianion were studied by passing the helium used as buffer gas for the ion trap over a small amount of the reagent of interest. The room-temperature vapor pressure of the reagents studied was sufficient to introduce a small concentration in the buffer gas. In this way, both heavy water and benzene could be reacted with the dianion. Reaction with heavy water produced a singly-deuterated monanion with m/z 126. Reaction with benzene produced the phenyl anion, identified from its m/z of 77, highlighting the extreme basicity of the dianion. Attempted reaction with deuterium gas and deuterated methane was not successful despite the favourable thermodynamics of the reactions, attributable to the high activation barrier for proton abstraction from those acids.[1]
Other isomers
Using the same method, the meta and para isomers of the dianion could also be produced. These were found to be less basic than the ortho isomer, the meta isomer having a proton affinity of 1786.8 kJ/mol, and the para isomer 1780.7 kJ/mol. The much greater basicity of the ortho isomer was attributed to Coulombic repulsion between the adjacent negative charges.[1]
References
- ^ a b c d e Poad, Berwyck L. J.; Reed, Nicholas D.; Hansen, Christopher S.; Trevitt, Adam J.; Blanksby, Stephen J.; Mackay, Emily G.; Sherburn, Michael S.; Chan, Bun; Radom, Leo (2016). "Preparation of an ion with the highest calculated proton affinity: ortho-diethynylbenzene dianion". Chem. Sci. 7 (9): 6245–6250. doi:10.1039/C6SC01726F.
- ^ Bergius, Will (19 July 2016). "Basically record breaking". Chemistry World.
- ^ Oliveira, Allan M.; Lu, Yu-Ju; Lehman, Julia H.; Changala, P. Bryan; Baraban, Joshua H.; Stanton, John F.; Lineberger, W. Carl (2015). "Photoelectron Spectroscopy of the Methide Anion: Electron Affinities of •CH3 and •CD3 and Inversion Splittings of CH3– and CD3–". J. Am. Chem. Soc. 137 (40): 12939–12945. doi:10.1021/jacs.5b07013.
- ^ Tian, Zhixin; Chan, Bun; Sullivan, Michael B.; Radom, Leo; Kass, Steven R. (2008). "Lithium monoxide anion: A ground-state triplet with the strongest base to date". PNAS. 105 (22): 7647–7651. doi:10.1073/pnas.0801393105.
