Timothy Alligrant - Acid/base and hydrogen bonding effects on the proton-coupled electron transfer of quinones and hydroquinones in acetonitrile: Mechanistic investigation by voltammetry, 1H NMR and computation

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      Publication Details (including relevant citation   information):

      Electrochim. Acta 2010, 55,   6507-6516.


      This report seeks to address the role of hydrogen bonding with   Brønsted acids and bases in proton-coupled electron transfer   (PCET) as it pertains to concerted or stepwise  pathways of quinone (Q) and hydroquinone (QH2)   electrochemistry. This study was performed using a series of   techniques that included cyclic voltammetry (CV), digital   simulations, computational chemistry and 1H NMR.   Hydrogen bonding was inferred by a decrease in diffusion   coefficient (D) values measured using a pulsed gradient   echo- (PGE-) 1H NMR technique. Changes of 40.8% and   37.9% in D values were only noted after the addition of   two equivalents of acetate to 1,4-hydroquinone   (1,4-QH2) and catechol (1,2-QH2),   respectively. In contrast, the D values for the addition   of selected amines (pyridine, N,N-diisopropylethylamine and   triethylamine) changed only 3.2% on average. Quantum mechanical   calculations were conducted to determine the   pKa of all quinoid species to serve as a   starting point for the determination of equilibrium constants in   voltammetric simulations. Simulations indicate that   1,4-benzoquinone undergoes stepwise electron–proton   transfer upon addition of acetic acid, N-ethyldiisopropylammonium   perchlorate and pyridinium nitrate and were simulated without the   presence of hydrogen bonds. The QH2 compounds show   stepwise proton–electron transfers after addition of the   both the conjugate amines and acetate.


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