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Physical Chemistry

New world champion base is crowned

o-Diethynylbenzene dianion has the highest gas-phase proton affinity of any molecule prepared to date

by Stephen K. Ritter
August 1, 2016 | A version of this story appeared in Volume 94, Issue 31

By preparing the o-diethynylbenzene dianion in a gas-phase experiment, a research team in Australia has set a record for the world’s strongest chemical base—a record the researchers suggest may be difficult to ever break (Chem. Sci. 2016, DOI: 10.1039/c6sc01726f). When it comes to strong acids and bases, sulfuric acid and sodium hydroxide typically come to mind. These substances are certainly strong and corrosive, Berwyck Poad of Queensland University of Technology and coworkers note. But as the researchers explain, acid and base strengths are typically measured by a molecule’s proton affinity, which is the amount of energy given off when a molecule binds a hydrogen ion. By this measure, a hydroxide anion has the largest proton affinity in aqueous solution at 1,633 kJ/mol. But in the gas phase, the strongest base until now was the lithium monoxide anion, with a proton affinity of 1,782 kJ/mol. To make the new record holder, Poad and coworkers first used a computational model to search for multiply charged anions as the strongest possible bases that might be stable enough to prepare. With diethynylbenzene dianions identified as a target, the researchers developed a process to make them by sequentially ionizing dicarboxylic acid precursors in a mass spectrometer. They show that the o-diethynylbenzene isomer is the strongest, with a proton affinity of 1,843 kJ/mol, which is enough to deprotonate benzene in the gas phase, and likely any other challenger.


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