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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 was prototypical in the study of free-radical additions. Early chemists discovered that the reason for the variability in the ratio of ...
Can occur either in syn or anti addition fashion depending on the specific mechanism followed. If osmium tetroxide is used, hydroxide groups are added in syn fashion. If an epoxide mechanism is followed, hydroxide groups are added in an anti fashion. Neither Markovnikov or anti-Markovnikov because the substituents are the same. Hydrobromination
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 ...
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 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.
Anne Troelstra [2] proved that it is an admissible rule in Heyting arithmetic. Later, the logician Harvey Friedman showed that Markov's rule is an admissible rule in first-order intuitionistic logic, Heyting arithmetic, and various other intuitionistic theories, [3] using the Friedman translation.
[3]: 188, 751 The result is typically anti-Markovnikov addition, a phenomenon Morris Kharasch called the "peroxide effect". [4] Reaction is slower with alkynes than alkenes. [3]: 750 In the paradigmatic example, hydrogen bromide radicalyzes to monatomic bromine. These bromine atoms add to an alkene at the most accessible site, to give a ...