20.11 : 自由基反应性： 亲电自由基

Electrophilic radicals have an electron-withdrawing group attached to the radical center. These radicals readily react with nucleophilic alkenes.

For instance, the malonate radical, formed from diethyl choloromalonate, reacts quickly with vinyl ether, which possesses an electron-donating oxygen substituent.

This reaction is favored because the electron-deficient, electrophilic radical has a low-energy SOMO, which readily interacts with the high-energy HOMO of the electron-rich, nucleophilic alkene.

Similar SOMO-HOMO interactions are also observed for non-carbon-centered radicals.

For instance, when a chlorine radical reacts with propionic acid, it abstracts a hydrogen from the terminal carbon.

This happens because the low-energy SOMO of the electrophilic chlorine radical interacts well with the high-energy HOMO of the C–H bond of the terminal methyl group.