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  • 1
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Two mechanistic pathways have been proposed for halogen atom transfer from the benzylic positions of halomethylarenes to triorganotin radicals. These are direct atom abstraction, which might involve an extremely polar transition state, and single electron transfer followed by bond cleavage. AM1 semi-empirical calculations have been utilized to model the rate-determining step of these processes. A wide range of related families of compounds have been studied, including substituted halomethylbenzes, selected halomethyl-substituted polycyclic aromatic hydrocarbons and oxygen- and nitrogen-containing chloromethyl-substituted heteroaromatic systems. Although these calculations are relatively simple, the present results corroborate the view that chlorine and bromine atom transfer from the benzylic position to triorganotin radicals involves a direct atom abstraction in the rate-determining step whereas reduction of the corresponding iodides proceeds via an electron-transfer mechanism.
    Additional Material: 8 Tab.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989), S. 367-376 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The relative rates of hydrogen atom abstraction from a series of twelve saturated cyclic ethers and sulfides were determined at 70°C. The abstracting radical could be generated from bromotrichloromethane both photolytically or by the thermal decomposition of AIBN. The reaction rates did not show a dependence upon method of radical generation. Reaction occurred only at the position adjacent to the heteroatom. The reactivity of the cyclic ethers was in the order C4H8O 〉 C6H12O 〉 C3H6O 〉 C5H10O. This trend would indicate appreciable influence by ring strain, however, the slightly greater reactivity of tetrahydrofuran relative to oxepane suggests a contribution by stereoelectronic factors as well. The reactivity of the cyclic sulfides, which reacted faster than the corresponding ethers, was in the order C4H8S 〉 C5H10S 〉 C6H12S. This would imply little influence of ring strain. The major structural effect would be that of variable electron donating ability of the sulfur atom. The rate of reaction of thietane was also determined. It was found to preferentially undergo SH2 attack at the sulfur atom followed by ring opening rather than hydrogen abstraction. The reactivities of both series of compounds were decreased by the inductive effect of a second heteroatom beta to the reaciton site.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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