In this work we describe how electrochemical measurements in non-aqueous solvents can be used to measure hydrogen-bonding abilities of electroactive and electroinactive compounds. The half-wave potentials or peak potentials measured using voltammetry are surprisingly very sensitive to hydrogen-bonding interactions, more so than spectroscopic methods such as UV-vis, NMR and FTIR. However, several important criteria need to be satisfied to enable the hydrogen-bonding interactions to be studied by electrochemistry. First, either the donor and/or acceptor must be electroactive. Second, the electron transfer kinetics should be reasonably fast so that the voltammetric data is not distorted. Third, the redox couple must be able to significantly influence the binding between the donor and acceptor. And last, the effects of proton-transfer can be differentiated from those of hydrogen bonding. A characteristic feature of hydrogen bonding is that it does not alter the chemical reversibility of the redox process, which may occur for proton-transfer reactions.<br/><br/>Quinones are the most widely studied molecules that undergo hydrogen-bonding through the electronegative oxygen atoms produced during the reduction processes. In aprotic organic solvents, quinones are able to undergo two one-electron reduction processes forming the radical anions (semiquinones) and then the dianions. It has been observed that the dianions are much more sensitive to hydrogen-bonding effects, which results in the second reduction process shifting towards more positive potentials as hydrogen bond donors (such as water) are added to the solution, until the first and second processes merge into one two-electron voltammetric wave. The chemical processes associated with the merging of the voltammetric waves will be discussed along with analytical uses of this effect, such as in quantifying the water content of organic solvents.

Using voltammetry to detect hydrogen-bonding interactions

253rd National Meeting (2017)

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