Graduate Thesis Or Dissertation
 

Hydrogen abstractions from arylmethanes

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  • The relative rates of hydrogen abstraction from a series of 13 arylmethanes by the trichloromethyl radical were determined at 70°. The attacking radical was generated from bromotrichloromethane us ing benzoyl peroxide as the initiator. The solvent was benzenebromotrichloromethane. An excellent correlation, with a coefficient of 0.977, was obtained when the logs of the relative rates of hydrogen abstraction were plotted against the change in pi-binding energy between the incipient radicals and the arylmethanes, if the pi-binding energy were calculated by the SCF approach. When the logs of the kinetic data were correlated with the change in pi-binding energy as calculated by the HMO approach, the correlation was poor, with a coefficient of 0.855. A possible explanation for this difference might be the Huckel method's complete neglect of electron interactions. The kinetic data were also plotted against the values of a parameter, ∑IR⁻³, which are indicative of the ground state electronic environment of the methyl group. A correlation was essentially nonexistent. This, coupled with the excellent correlation with the changes in pi-binding energies, indicates that the transition state for hydrogen abstraction by the trichloromethyl radical must certainly lie near the intermediate radical with carbon-hydrogen bond breaking well advanced. The relative rates of hydrogen abstraction from a series of nine arylmethanes by the t-butoxy radical were also determined at 70°. t-Butoxy radical was generated from t-butyl hypochlorite using benzoyl peroxide as the initiator. The solvent was benzene. Best agreement was obtained when the data was correlated with a four parameter equation which included both the change in pi-binding energy and ∑IR⁻³. This is tentatively taken to mean that the transition state is at a point intermediate between the reactants and the intermediate radicals.
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Déclaration de droits
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  • File scanned at 300 ppi (Monochrome) using ScandAll PRO 1.8.1 on a Fi-6770A in PDF format. CVista PdfCompressor 5.0 was used for pdf compression and textual OCR.
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