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In organic chemistry, a radical-substitution reaction is a substitution reaction involving free radicals as a reactive intermediate. [1] The reaction always involves at least two steps, and possibly a third. In the first step called initiation (2,3), a free radical is created by homolysis.
Substitution reactions in organic chemistry are classified either as electrophilic or nucleophilic depending upon the reagent involved, whether a reactive intermediate involved in the reaction is a carbocation, a carbanion or a free radical, and whether the substrate is aliphatic or aromatic. Detailed understanding of a reaction type helps to ...
This reaction type was discovered in 1970 by Bunnett and Kim [3] and the abbreviation S RN 1 stands for substitution radical-nucleophilic unimolecular as it shares properties with an aliphatic S N 1 reaction. An example of this reaction type is the Sandmeyer reaction.
include such reactions as halogenation, hydrohalogenation and hydration. nucleophilic addition: radical addition: Elimination reaction: include processes such as dehydration and are found to follow an E1, E2 or E1cB reaction mechanism: Substitution reactions: nucleophilic aliphatic substitution: with S N 1, S N 2 and S N i reaction mechanisms
Radical elimination can be viewed as the reverse of radical addition. In radical elimination, an unstable radical compound breaks down into a spin-paired molecule and a new radical compound. Shown below is an example of a radical elimination reaction, where a benzoyloxy radical breaks down into a phenyl radical and a carbon dioxide molecule. [7]
These reactions can happen due to the free radicals having an unpaired electron in their valence shell, making them highly reactive. [1] Radical additions are known for a variety of unsaturated substrates, both olefinic or aromatic and with or without heteroatoms. Free-radical reactions depend on one or more relatively weak bonds in a
Intramolecular free radical reactions (substitution or addition) such as the Hofmann–Löffler reaction or the Barton reaction; Free radical rearrangement reactions are rare compared to rearrangements involving carbocations and restricted to aryl migrations. Fragmentation reactions or homolysis, for instance the Norrish reaction, the ...
N-Bromosuccinimide or NBS is a chemical reagent used in radical substitution, electrophilic addition, and electrophilic substitution reactions in organic chemistry. NBS can be a convenient source of Br •, the bromine radical. [1]