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Formation of CC Bonds by Addition of Free Radicals to Alkenes

Authors

  • Prof. Dr. Bernd Giese

    Corresponding author
    1. Institut für Organische Chemie und Biochemie der Technischen Hochschule, Petersenstrasse 22, D-6100 Darmstadt (Germany)
    • Institut für Organische Chemie und Biochemie der Technischen Hochschule, Petersenstrasse 22, D-6100 Darmstadt (Germany)
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  • Dedicated to Professor Karl Winnacker on the occassion of his 80th birthday

Abstract

There are many reactions in which CC bonds are formed by addition of free radicals to alkenes. Information about the mechanism is important for the synthesis of specific target molecules. The rate of addition of alkyl radicals to alkenes is controlled by steric and polar effects. The stabilities of the educts and products are of only limited importance, since the transition states for these exothermic reactions occur very early on the reaction coordinate. Variations in reactivity and selectivity can be described using frontier orbital theory: for nucleophilic radicals the dominant interactions are those between SOMO's and LUMO's, and for electrophilic radicals those between SOMO's and HOMO's. The large differences in the steric effects of α - and β- substituents of alkenes can be explained by postulating an unsymmetrical transition state— the radical approaches one of the C atoms preferentially. Regioand stereoselectivities can be predicted and are determined, in general, by steric effects.

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