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Anti-Markovnikov behaviour is observed in the hydration of phenylacetylene by auric catalysis, which gives acetophenone; although with a special ruthenium catalyst [8] it provides the other regioisomer 2-phenylacetaldehyde: [9] Anti-Markovnikov hydration. Anti-Markovnikov behavior can also manifest itself in certain rearrangement reactions.
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]
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.
The addition proceeds in an anti-Markovnikov fashion. Early work linked the addition to olefin polymerization. [4] This addition is a step in a protocol known as atom transfer radical polymerization. [5] An example of Kharasch addition is the synthesis of 1,1,3-trichloro-n-nonane from 1-octene and chloroform using an iron-based catalyst: [6]
Hydrosilylation of alkenes usually proceeds via anti-Markovnikov addition, i.e., silicon is placed at the terminal carbon when hydrosilylating a terminal alkene; [1] however, in the recent years, Markovnikov addition has become a growing field of research.