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Such reactions are said to be anti-Markovnikov, since the halogen adds to the less substituted carbon, the opposite of a Markovnikov reaction. The anti-Markovnikov rule can be illustrated using the addition of hydrogen bromide to isobutylene in the presence of benzoyl peroxide or hydrogen peroxide. The reaction of HBr with substituted alkenes ...
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Hydroboration–oxidation is an anti-Markovnikov reaction, with the hydroxyl group attaching to the less-substituted carbon. The reaction thus provides a more stereospecific and complementary regiochemical alternative to other hydration reactions such as acid-catalyzed addition and the oxymercuration–reduction process.
In terms of regiochemistry, hydroboration is typically anti-Markovnikov, i.e. the hydrogen adds to the most substituted carbon of the double bond. That the regiochemistry is reverse of a typical HX addition reflects the polarity of the B δ+-H δ− bonds. Hydroboration proceeds via a four-membered transition state: the hydrogen and the boron ...
In the presence of peroxides, HBr adds to a given alkene in an anti-Markovnikov addition fashion. Regiochemistry follows from the reaction mechanism, which exhibits halogen attack on the least-hindered unsaturated carbon.
The reaction follows Markovnikov's rule (the hydroxy group will always be added to the more substituted carbon). The oxymercuration part of the reaction involves anti addition of OH group but the demercuration part of the reaction involves free radical mechanism and is not stereospecific, i.e. H and OH may be syn or anti to each other. [2] [3] [4]
In 1869, a Russian chemist named Vladimir Markovnikov demonstrated that the addition of HBr to alkenes usually but not always resulted in a specific orientation. Markovnikov's rule, which stems from these observations, states that in the addition of HBr or another hydrogen halide to an alkene, the acidic proton will add to the less substituted carbon of the double bond. [3]
The reaction mechanism involves free radicals of the general formula CXCl 2 (X = Cl, H). For the precursors carbon tetrachloride and chloroform, the requisite radicals can arise by abstraction of a halogen atom by a electropositive metal. The addition proceeds in an anti-Markovnikov fashion. Early work linked the addition to olefin polymerization.