Relation between the First and the Second Nonaqueous Reduction Potentials of Substituted Stilbenes

概要

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The nonaqueous reduction polarograms of 4,4'-disubstituted stilbenes exhibited two waves, the half-wave reduction potentials, E^<red>_<1/2・1> and E^<red>_<1/2・2>, of which are mainly controlled at the steps of monoanion and dianion formation, respectively. The physical meanings of E^<red>_<1/2・1> and E^<red>_<1/2・2> can be clearly seen by applying the Born-Haber type thermochemical cycle and molecular orbital (MO) calculation, and theoretical equations concerning (E^<red>_<1/2・1>+E^<red>_<1/2・2>) and (E^<red>_<1/2・1>-E^<red>_<1/2・2>) were formulated. The MO calculations of the PPP-SCFMO, LP-SCFMO, and CNDO/2 levels were used for checking the formulae. The results were quite reasonable on the assumption that the contribution from the solvation energy terms is almost constant or alters in parallel with the LUMO energy in a series of similar substances. In the case of NO_2 as a substituent, as in 4,4'-dinitrostilbene, the E^<red>_<1/2・2> value is markedly shifted in a negative direction from that expected from the other substituents, so that the NO_2 group does not fit well with the above theoretical treatment. High-speed cyclic voltammetric measurements were performed to investigate this phenomenon of nitro-substituted aromatics, and the results are discussed in detail.
公益社団法人日本薬学会の論文
1984-01-25