Enhanced proton loss from neutral free radicals : toward carbon-centered superacids
Abstract
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.
Citation
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
Publication
Journal of Physical Chemistry A
Status
Peer reviewed
ISSN
1089-5639Type
Journal article
Description
J.C.W. thanks EaStCHEM for financial support.Collections
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