Abstract
The effect of substituents on π radical reactions of para-substituted tetraphenylporphyrins was investigated by cyclic voltammetry in methylene chloride. In all cases electron donating substituents produced a more difficult reduction and an easier oxidation. Plots of E 1 2 vs. σ yielded Hammett linear free energy relationships for cation radical and dication formation and anion radical and dianion formation. An average reaction constant of ϱ = 0.07 ± 0.01 V was obtained. This was true for tetraphenylporphyrins containing the central metals VO, Mn, Fe, Co, Ni, Cu, and Zn, as well as the free base H 2 ( p-X)TPP. The value of ϱ appears not to be directly affected by the central metal oxidation state or the overall charge on the complex.
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