VARIATION OF THE HALF-WAVE POTENTIAL OF ORGANIC COMPOUNDS WITH pH. Report No. 78
From 19th International Union of Pure and Applied Chemistry Congress, London. A systematic introduction is presented to the subject of the variation with pH of the polarographic half-wave potential, which is probably the most readily measured electrochemical energetic parameter of organic compounds. Emphasis is placed on (a) the types of relationships observed for both reversible and irreversible electrode processes, (b) the mathematical formulation of these relationships, (c) the structural, mechanistic, kinetic, and environmental factors influencing such relationships, and (d) the presumptive physical causes for such relationships, e.g., the effect of pH on the electrochemical kinetics. Although the discussion is primarily concerned with behavior in aqueous solution, the conclusions drawn are equally valid for nonaqueous media in which hydrogen ion or some other Lewis acid can play a significant role. The half-wave potential for an organic electrode process may be independent of pH, or may vary lineanly or sigmoidally; other types of relationships observed are likely to be combinations of such effects. These variations may be due (a) to direct participation of hydrogen ion in the transition state involving the electroactive site in the organic molecule and the electron source, e.g., polarization of the bond to be broken, (b) to control of the state of reactants and/or products via participation in pre- and postequilibria, e.g., acid-base equilibria affecting the nature of the reactant or (c) to the effects of other kinetic, adsorption, steric, hydrogen-bonding and electrical double layer phenomena, as well as to combinations and variations of these effects. Solution composition factors influencing the observed variation of half-wave potential with pH include the ionic strength, the nature of the solvent, the specific identity of buffer components, and nonspecific salt effects. The implications of the experimentally observed half-wave potential-pH relations are considered in respect to the development of analytical procedures and the correlation of half-wave potential data. (auth)
- Research Organization:
- Michigan. Univ., Ann Arbor. Dept. of Chemistry
- Sponsoring Organization:
- US Atomic Energy Commission (AEC)
- DOE Contract Number:
- AT(11-1)-1148
- NSA Number:
- NSA-17-033867
- OSTI ID:
- 4670260
- Report Number(s):
- CONF-151-2
- Resource Relation:
- Conference: 19th International Union of Pure and Applied Chemistry Congress, London, June 21, 1963; Other Information: From 19th International Union of Pure and Applied Chemistry Congress, London. Orig. Receipt Date: 31-DEC-63
- Country of Publication:
- United States
- Language:
- English
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