Molecular orbital considerations on the reactivities of vinyl compounds. III. Polarographic reduction

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Abstract
The polarographic half‐wave reduction potentials E1/2 of several vinyl (including vinylidene) monomers were measured and were discussed on the basis of the molecular orbital theory. The current‐voltage curves were determined in a 0.05 M solution of tetra‐n‐butylammonium iodide in the mixture of dioxane and water (3:1 by volume). The values of E1/2 were read against the saturated calomel electrode. It was found that E1/2 is correlated with xiv by E1/2 = 2.33 xiv−0.80, where xiv stands for the root of the MO secular equation for the π‐electronic system of the vinyl monomer corresponding to the lowest vacant level. Some of the monomers could not be reduced in the range of the applied potential less negative than − 3.0 volt vs. SCE, which was reasonably explained by their relatively large values of −xiv. It was suggested that the polarographic reducibility of vinyl monomers is roughly parallel to their anionic polymerizability. Furthermore, the lowest vacant π‐orbital energies of vinyl compounds were calculated according to the first order perturbation method. The results obtained thus were in good accordance with those calculated directly from the secular equations. It was also shown that the first ionization potentials of vinyl compounds were roughly related to their highest occupied π‐electronic energies.

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