Molecular orbital considerations on the reactivities of vinyl compounds. II. Ionic polymerizability

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Abstract
The β‐carbon localization energies Lβ+ and Lβ− for electrophilic and nucleophilic additions to vinyl compounds, respectively, were calculated according to the simple LCAO MO method and were compared with the experimental results so far reported on the ionic polymerizability of these compounds. The larger the cationic (or anionic) polymerizability of a monomer, the smaller was the value of Lβ+ (or Lβ−) for it. It was also verified in terms of localization energies that the vinyl monomers which are not amenable to radical polymerization tend to polymerize more easily by either of the two ionic mechanisms. By applying Jaffé's first order perturbation method, Lβ+ and Lβ− of each monomer were expressed as functions of the Coulomb integral parameters of the heteroatoms involved. Although the values of Lβ+ and Lβ− did not agree perfectly with the direct results obtained from secular equations, the discrepancy in both cases could be minimized when each of the Coulomb integral parameters employed in the perturbation approximation was empirically taken as 0.6 times as large as that used in the direct variation calculation. The procedure was successfully applied to the interpretation of the substituent effect on the cationic polymerizability of styrene.

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