Ion Radicals of Methylhyphen;Substituted Benzenes: Temperature Dependence of Spin and Charge Densities

摘要

The spin and charge densities for the monomethyl and dimethyl benzene negative ions are calculated with the valencehyphen;bond perturbation procedure developed previously. Because the difference in energy (Dgr;E) between the two lowest eigenvalues of these systems is found to be small, thermal averaging is included in the determination of the theoretical spin densities.Metahyphen;xylene negativehyphen;ion data are used to evaluate the required valencehyphen;bond parameters. Comparison of the measured and calculated hyperfine constant values, including the available temperaturehyphen;dependence data, shows good agreement in most cases. However, a number of discrepancies appear to exist and further investigation is required. The experimental and theoretical difficulties in obtaining good Dgr;Evalues are also discussed.The formulation is used to predict spin densities for some unknown methylhyphen;substituted benzene negative ions and for the methylhyphen;substituted benzene positive ions. Also, values are obtained for the perturbation parameter (Dgr;Cxmdash;) for the other alkylhyphen;substituted benzene negative ions which have been studied experimentally. Some discussion is given concerning the extension of the treatment to systems other than substituted benzene ionhyphen;radicals. The reliability of the method is considered, and comparisons are made with available moleculehyphen;orbital calculations.