Using Voltammetry to Measure the Relative Hydrogen-Bonding Strengths of Pyridine and Its Derivatives in Acetonitrile

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review

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Author(s)

  • Malcolm E. Tessensohn
  • Yu Rong Koh
  • Sihao Lim
  • Hajime Hirao
  • Richard D. Webster

Detail(s)

Original languageEnglish
Pages (from-to)2250-2257
Number of pages8
Journal / PublicationChemPhysChem
Volume18
Issue number16
Online published28 Jun 2017
Publication statusPublished - 18 Aug 2017
Externally publishedYes

Abstract

The voltammetric behavior of 2,3,5,6-tetramethyl-1,4-phenylenediamine was found to be able to differentiate the hydrogen acceptor abilities of electroinactive pyridine compounds in acetonitrile. Weak and strong hydrogen acceptors were distinguished through the onset of a third oxidation process that came about at sub-stoichiometric amounts of strong hydrogen acceptors, but not in the presence of weak hydrogen acceptors. This additional oxidation reaction occurred at a potential between the two 1e--oxidation reactions that phenylenediamines typically undergo (i.e. EP ox(1)<EP ox(3)<EP ox(2), with EP ox(1) and EP ox(2) representing the electrochemical conversion of the neutral phenylenediamine into the radical cation and thereafter to the quinonediimine dication) as well as at the expense of the second electrochemical reaction. EP ox(2) and EP ox(3) were observed to shift towards less positive potentials with increasing concentrations of weak or strong hydrogen acceptors, respectively, whereas EP ox(1) remained virtually unaffected. This allows the electrochemical parameters ΔEP ox(1,2)=|EP ox(1)-EP ox(2)| and ΔEP ox(1,3)=|EP ox(1)-EP ox(3)| to be employed as measures of the hydrogen-bonding strengths within each category, to which they were found to be highly reproducible and responsive to steric, electronic, inductive, and mesomeric effects. The electrochemical findings concur with available aqueous pKa data of the protonated pyridine compounds but were, however, in poor agreement with results obtained by density functional theory calculations.

Research Area(s)

  • Basicity, Electrochemistry, Hydrogen acceptor, Phenylenediamine, Voltammetry

Citation Format(s)

Using Voltammetry to Measure the Relative Hydrogen-Bonding Strengths of Pyridine and Its Derivatives in Acetonitrile. / Tessensohn, Malcolm E.; Koh, Yu Rong; Lim, Sihao; Hirao, Hajime; Webster, Richard D.

In: ChemPhysChem, Vol. 18, No. 16, 18.08.2017, p. 2250-2257.

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review