Radical Site Shift
Radical Site Shift - Related Videos
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Radicals adjacent to electron-donating groups are called nucleophilic radicals. These radicals readily react with electrophilic alkenes. The SOMO–LUMO interactions are the driving force for the reaction, where the high-energy SOMO of the electron-rich, nucleophilic radicals interacts with the low-energy LUMO of the electron-deficient, electrophilic alkenes. Such SOMO–LUMO interactions are the basis of reactive radical traps, affecting the selectivity in radical reactions. For instance, consider...
FAQs
An initially generated radical abstracts a hydrogen atom from another position within the same molecule. In a 1,5- or 1,6-hydrogen-atom transfer, the atoms can interact through a favorable cyclic transition state. Removing hydrogen breaks the original C–H bond and produces a new carbon-centered radical at a remote location, relocating the site available for subsequent reaction.
These hydrogen-atom transfer pathways provide the cyclic arrangements required for intramolecular abstraction. Their importance lies in converting an initial radical into a distinct, remote carbon-centered radical without first forming a bond between separate molecules. The resulting intermediate can then undergo a selective transformation at a position that may otherwise remain unreactive.
Radical site shifts use a sequence of radical intermediates to relocate reactivity before the key transformation occurs. This behavior differs from conventional ionic reactions, which may not provide a comparable route to remote carbon sites. As a result, the strategy can support carbon–hydrogen functionalization and access molecular structures that are difficult to obtain through ionic pathways.
The sequence begins by generating an initial radical within a molecule, followed by intramolecular hydrogen-atom transfer. That step creates a new radical at a remote carbon position. The relocated intermediate is then directed into a chosen trapping or transformation pathway, such as bond formation, halogenation, oxidation, or reduction, depending on the reaction design.
A remote carbon-centered radical provides several possible reaction outcomes. It may form a new bond, undergo halogenation, or participate in oxidation or reduction. These options allow the site shift to serve as a strategic intermediate-forming step rather than an isolated rearrangement, connecting radical relocation with broader synthetic goals and diverse product structures.
This strategy is useful when a synthesis requires modification of a carbon–hydrogen bond at a site that is difficult to reach directly. By relocating radical reactivity within the molecule, chemists can target remote positions and build structures that conventional ionic reactions may not readily provide. Its value therefore centers on selective remote functionalization and expanded synthetic access.