| Abstract
| - The electrochemical behavior of a series of symmetrical and unsymmetrical aryl-substitutedacetophenone azines (1-X/Y, where X and Y are 4-NO2, 4-CN, H, 3-OCH3, 4-OCH3, 4-CH3, and4-N(CH3)2) was studied in acetonitrile and N,N-dimethylformamide (DMF) solution using cyclicvoltammetry (CV). Compounds 1-X/Y, where neither X or Y are nitro substituents, undergosuccessive reduction to their radical anion (1-X/Y•-) and then dianion (1-X/Y2-), respectively. In allcases, the formation of the radical anion is completely reversible and the standard reductionpotentials, E°1-X/Y/1-X/Y•− could be determined. The reversibility of the second electron transfer issubstituent dependent with certain dianions sufficiently basic to be protonated under our conditions.Standard reduction potentials (E°1-X/Y/1-X/Y•−) for the formation of radical anions exhibit a largesubstituent effect with values differing by more than 0.66 V throughout the series going from 1-4-CN/4-CN to 1-4-OCH3/4-OCH3; similar substituent effects were determined for the formation ofthe dianion. The nitro-containing azines deviate from the above-mentioned behavior. With theexception of 1-4-NO2/4-NO2, they exhibit single electron waves that have values of E°1-X/Y/1-X/Y•−within 40 mV of each other and thus the reduction is not subject to the same substituent effect asthe other azines. 1-4-NO2/4-NO2 exhibits an E° at a similar potential, but is a two-electron reversiblewave with features indicative of a reduction system containing two localized, nonconjugated redoxcenters. The reduction potentials of all the aryl azines were correlated with Hammett σ parametersto look at variations in E°1-X/Y/1-X/Y•− vs SCE as a function of substituent. The small ρ values incombination with the other electrochemical data provide support for single bond character of theN−N bond and evidence for a lack of strong electronic communication between the two aryl centersthrough the azomethine bonds, especially for those systems with electron-withdrawing groups.
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