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Radical addition of hydrogen bromide is a valuable synthetic technique for anti-Markovnikov carbon substitution, [citation needed] but free-radical addition does not occur with the other hydrohalic acids. Radical formation from HF, HCl, or HI is extremely endothermic and chemically disfavored.
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]
In this type of substitution reaction, one group of the substrate participates initially in the reaction and thereby affects the reaction. A classic example of NGP is the reaction of a sulfur or nitrogen mustard with a nucleophile, the rate of reaction is much higher for the sulfur mustard and a nucleophile than it would be for a primary or secondary alkyl chloride without a heteroatom.
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.
Radical addition of a bromine radical to a substituted alkene. In free-radical additions, a radical adds to a spin-paired substrate. When applied to organic compounds, the reaction usually entails addition to an alkene. This addition generates a new radical, which can add to yet another alkene, etc. This behavior underpins radical ...
Typical bases are triethylamine, potassium carbonate, and sodium acetate. The aryl electrophile can be a halide (Br, Cl) or a triflate as well as benzyl or vinyl halides. The alkene must contain at least one sp 2-C-H bond. Electron-withdrawing substituents enhance the reaction, thus acrylates are ideal. [12]
General overview of addition reactions. Top to bottom: electrophilic addition to alkene, nucleophilic addition of nucleophile to carbonyl and free-radical addition of halide to alkene. Depending on the product structure, it could promptly react further to eject a leaving group to give the addition–elimination reaction sequence.
A reported reaction of alkene acrylic acid with an aryl diazonium salt and copper(I) bromide and hydrobromic acid yields the α-bromocarboxylic acid. [4] When the alkene is butadiene the initial reaction product with catalyst copper(II) chloride is a 4-chloro-2-butene and after an elimination the aryl substituted butadiene. [5]