Anti Markovnikov Addition
Anti Markovnikov Addition - Related Videos
01:17
Radical Anti-Markovnikov Addition to Alkenes: Mechanism
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2025
The reaction of hydrogen bromide with alkenes in the presence of hydroperoxides or peroxides proceeds via anti-Markovnikov addition. The radical chain reaction comprises initiation, propagation, and termination steps. The mechanism starts with chain initiation, which involves two steps. In the first chain initiation step, a weak peroxide bond is homolytically cleaved upon mild heating to form two alkoxy radicals. In the second initiation step, a hydrogen atom is abstracted by the alkoxy radical...
01:25
Radical Anti-Markovnikov Addition to Alkenes: Overview
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2023
The addition of hydrogen bromide to alkenes in the presence of hydroperoxides or peroxides proceeds via an anti-Markovnikov pathway and yields alkyl bromides. The observed regioselectivity can be explained based on the radical stability and steric effect. From the radical stability perspective, adding hydrogen bromide in the presence of peroxide directs the bromine radical at the less substituted carbon via a more stable tertiary radical intermediate. Similarly, in the steric framework, the...
01:32
Radical Anti-Markovnikov Addition to Alkenes: Thermodynamics
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2025
The anti-Markovnikov addition of hydrogen halides to an alkene is thermodynamically feasible only with HBr. The radical addition reaction with other hydrogen halides like HCl and HI is thermodynamically unfavorable. Thermodynamic factors The temperature influences the spontaneity of a reaction, which can be evaluated based on the change in the Gibbs free energy, ΔG. If the change in Gibbs free energy, ΔG, is negative, the reaction occurs spontaneously. As shown below, ΔG can be evaluated...
02:20
Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule
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2026
If a set of reactants can yield multiple constitutional isomers, but one of the isomers is obtained as the major product, the reaction is said to be regioselective. In such reactions, bond formation or breaking is favored at one reaction site over others. The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
01:27
Conjugate Addition (1,4-Addition) vs Direct Addition (1,2-Addition)
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2025
α,β-Unsaturated carbonyl compounds with two electrophilic sites, the carbonyl carbon, and the β carbon, are susceptible to nucleophilic attack via two modes: conjugate or 1,4-addition and direct or 1,2-addition. Conjugate addition results in a thermodynamically stable product. The reaction retains the stronger C=O bond at the expense of the weaker C=C π bond. The process is slow as the β carbon is less electrophilic than the carbonyl carbon. Direct addition products are formed faster owing to...
FAQs
In the hydrogen bromide–peroxide pathway, the orientation arises from formation of a carbon-centered radical intermediate. This intermediate forms preferentially at the more substituted carbon because it is more stable, so bromine becomes attached to the less substituted carbon. The observed regiochemistry therefore reflects intermediate stability under radical conditions, rather than a rule independent of mechanism.
Hydroboration followed by oxidation places the hydroxyl group on the less substituted carbon because the addition proceeds through a concerted syn mechanism. This pathway does not rely on the carbon-centered radical intermediate associated with hydrogen bromide and peroxides. Its concerted arrangement provides a route to less substituted alcohols while supporting control over both regiochemistry and stereochemical outcome.
Reaction conditions determine which mechanism operates and which substituent is introduced. Hydrogen bromide with peroxides produces a haloalkane in which bromine occupies the less substituted carbon through a radical intermediate. Hydroboration followed by oxidation instead produces an alcohol with hydroxyl at that position through concerted syn addition. Mechanism therefore links reagent choice to product structure.
The desired functional group provides the primary guide. For a less substituted haloalkane, the hydrogen bromide and peroxide pathway is appropriate because bromine is placed on the less substituted carbon. For a less substituted alcohol, hydroboration followed by oxidation provides the corresponding hydroxyl placement. Selecting conditions this way connects the starting unsaturated compound to the intended product type.
These reactions provide controlled access to less substituted alcohols and haloalkanes from unsymmetrical alkenes or alkynes. The hydroboration-oxidation route is associated with alcohol formation, whereas hydrogen bromide with peroxides gives a brominated product. Such control is valuable in organic synthesis because the position of the introduced functional group directly affects the structure of the resulting compound.
Its importance comes from combining predictable regiochemistry with mechanistic control. Chemists can use radical conditions when a less substituted carbon must receive bromine, or a concerted hydroboration-oxidation pathway when that carbon must receive hydroxyl. Studying these alternatives also shows how reaction mechanisms, intermediate stability, and syn addition help determine product structures in chemistry.