Polar effects in radical addition reactions: Borderline cases

✍ Scribed by Giese, Bernd ;He, Jianing ;Mehl, Wolf

• Publisher: Wiley (John Wiley & Sons)
• Year: 1988
• Tongue: English
• Weight: 288 KB
• Volume: 121
• Category: Article
• ISSN: 0009-2940
• DOI: 10.1002/cber.19881211127

✦ Synopsis

Methyl radicals substituted by one ester or nitrile group are on the borderline between nucleophilic and electrophilic behavior. In addition reactions of these borderline radicals to styrenes, polar effects of both, electron-withdrawing and electron-donating substituents at the alkeae, increase the rates. But these polar effects are smaller compared to those of nucleophilic or electrophilic radicals. In consequence, the stability of the radicals formed during the addition of the borderline radicals to styrenes are of major importance for the rate of the reaction.

Rates and selectivities of radical reactions are often ruled by polar effects'.*'. This is explained by the frontier molecular orbital (FMO) theory as an interplay between the SOMO of the radical and the LUMO or the HOMO of the In nucleophilic radical reactions SOMO-LUMO interactions dominate, whereas electrophilic radical reactions are controlled by SOMO-HOMO interactions.

We have now studied the question how radicals behave, which are on the borderline between nucleophilic and electrophilic reac-1 2 3 l a b c d e f g