Enhanced proton loss from neutral free radicals : toward carbon-centered superacids
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Radical centers close to protons are known to enhance their dissociation. Investigation of the generality of this radical enhanced deprotonation (RED-shift) phenomenon, and the kinds of structures in which it operates, are reported. The pKas for sulfinic, sulfonic, pentan-2,4-dione, and Meldrum's acid species, with adjacent radicals centered on C-, N-, and O atoms, were computed by a DFT method from free energies of deprotonation. All series showed significant RED-shifts that increased with the electronegativity of the radical center. The hugely negative pKa obtained for a Meldrum's acid with an alkoxyl radical substituent showed it to belong to the superacid class. The ethyne unit was found to be uniquely effective at enhancing acidity and conducting RED-shifts through chains up to and beyond 20 atoms. These connector units enable a radical center to alter the pKa of a spatially remote acidic group. RED-shifted species were characterized by conjugate radical anions displaying site exchange of spin with electronic charge.
Walton , J C 2018 , ' Enhanced proton loss from neutral free radicals : toward carbon-centered superacids ' , Journal of Physical Chemistry A , vol. 122 , no. 5 , pp. 1422-1431 . https://doi.org/10.1021/acs.jpca.7b11796
Journal of Physical Chemistry A
Copyright © 2018 American Chemical Society. This work has been made available online in accordance with the publisher’s policies. This is the author created accepted version manuscript following peer review and as such may differ slightly from the final published version. The final published version of this work is available at: https://doi.org/10.1021/acs.jpca.7b11796
DescriptionJ.C.W. thanks EaStCHEM for financial support.
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