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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 ...
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]
Markovnikov, who published in 1870 what is now known as Markovnikov's rule, and Zaytsev held conflicting views regarding elimination reactions: the former believed that the least substituted alkene would be favored, whereas the latter felt the most substituted alkene would be the major product.
In order for a reaction to follow Markovnikov's rule, the intermediate carbocation of the mechanism of a reaction must be on the more-substituted carbon, allowing the substituent to bond to the more-stable carbocation and the more-substituted carbon. [2] 1,2-disubstituted Cycloalkene undergoing syn and anti addition
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.
Markovnikov's rule predicts that the hydrogen atom is added to the carbon of the alkene functional group which has the greater number of hydrogen atoms (fewer alkyl substituents). Zaitsev's rule predicts that the major reaction product is the alkene with the more highly substituted (more stable) double bond.
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.
Zaitsev's Rule was reported in 1875, and appeared just as his nemesis, Markovnikov, (who had made a prediction which the rule contradicts) was taking the Chair at Moscow University. Zaytsev received several honors: he was elected as a Corresponding member of the Russian Academy of Science , an honorary member of Kiev University , and he served ...