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NBS reacts with alkenes in aqueous solvents to give bromohydrins. The preferred conditions are the portionwise addition of NBS to a solution of the alkene in 50% aqueous DMSO, DME, THF, or tert-butanol at 0 °C. [3] Formation of a bromonium ion and immediate attack by water gives strong Markovnikov addition and anti stereochemical selectivities ...
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.
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.
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.
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 ...