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How do free-radical addition reactions differ from electrophilic addition reactions?

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dissociation of E–N — reaction mechanism Possible energy diagram for the dissociation of a covalent molecule, E–N, into its ions E⁺ and N⁻ (see text).

Free-radical addition reactions and electrophilic addition reactions differ primarily in their mechanistic pathways and the nature of their intermediates.

Electrophilic Addition

Electrophilic addition typically involves polar intermediates. It begins with an electrophilic attack on an electron-rich center, such as a double bond. The electrophile (a positive ion or a polarized species) adds to the molecule, often forming a carbonium ion intermediate. Because these reactions are governed by the distribution of electrons, they are highly selective regarding the orientation of the initial attack.1

Free-Radical Addition

In contrast, free-radical addition reactions proceed via a homolytic mechanism, where reagents undergo fission to produce neutral atoms or radicals containing unpaired electrons. These reactions often involve chain processes where a single initiation step leads to the formation of many product molecules.23

Key differences include:
* Intermediates: Electrophilic additions involve charged ions (like carbonium ions), whereas free-radical additions involve neutral species with unpaired electrons.123
* Orientation: Free-radical mechanisms can result in an orientation of substituents that is opposite to that observed in electrophilic addition.2
* Chain Reactions: Free-radical additions are frequently characterized by chain-propagating sequences, which are not a feature of standard electrophilic addition.2