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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
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]
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 ...
For terminal olefins (or acetylenes), the regioselectivity of the process can be described as Markovnikov (addition of X at the substituted end) or anti-Markovnikov (addition of X at the unsubstituted end). Catalysts are frequently employed to control the chemo-, regio-, and stereoselectivity of hydrofunctionalization reactions.
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.
This addition reaction is typically facilitated by a radical initiator or UV irradiation and proceeds through a sulfanyl radical species. With monoaddition a mixture of (E/Z)-alkenes form. The mode of addition is anti-Markovnikov. The radical intermediate can engage in secondary reactions such as cyclisation.
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He defined the peroxide effect, explaining how an anti-Markovnikov orientation could be achieved via free radical addition. [1] Kharasch was born in the Russian Empire in 1895 and immigrated to the United States at the age of 13. In 1919, he completed his Ph.D. in chemistry at the University of Chicago and spent most of his professional career ...