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Alkenes are classified as unsaturated hydrocarbons because they contain at least one double bond in each molecule of the compound. These compounds exhibit additional reactions, which occur when an electrophile attacks the carbon-carbon double bond, resulting in the formation of additional products.Anti Markovnikov reactions are one of the few reactions in organic chemistry that are based on free radical mechanisms rather than electrophilic addition, as suggested by Markovnikov’s work. Hydrogen Bromide, but not Hydrochloric Acid, or HI, are the only chemicals that cause this reaction (Hydrogen Iodide).
Anti Markovnikov Addition
HBr is added to asymmetric alkenes in the existence of peroxide, resulting in the formation of 1-bromopropane, which is in opposition to the formation of 2-bromopropane (as dictated by Markovnikov’s rule). This reaction is also known as the anti-Markovnikov addition or the Kharash effect, after the scientist who discovered it, M. S. Kharash. The Kharash effect, also known as the peroxide effect, is a type of chemical reaction.
Anti-Markovnikov addition is also an illustration of an addition reaction of alkenes that is the exception to Markovnikov’s rule, and it is also an example of an addition reaction of alkenes. It is among the few reactions in organic chemistry that uses the free radical mechanism rather than electrophilic addition, as suggested by Markovnikov. This reaction can only be observed with HBr and not with HCl or HI.
(ORGANIC PEROXIDE)
CH3-CH=CH2+HBr ———————————–→CH3-CH(H)-CH2(Br)
Mechanism of Anti Markovnikov Addition
It has been discovered that the Anti Markovnikov addition reaction is governed by a free radical mechanism. The peroxide component that is involved contributes to the production of free radicals. The following section describes the general mechanism of the anti-Markovnikov addition reaction:
- The formation of free radicals occurs as a result of the homolytic cleavage of the peroxide molecule.
- Through hemolysis, the attack of a produced free radical on hydrogen halide results in the formation of a halide radical.
- Through hemolysis, the produced halide radical attacks the alkene molecule, resulting in the formation of an alkyl radical.
- Attack of an alkyl radical created on a hydrogen halide, resulting in the formation of alkyl halide through homolytic breakage of the hydrogen halide bond.
Diagram of Anti Markovnikov Addition
Anti-Markovnikov Rule
Rather than bonding to more carbon substitutes, the anti-Markovnikov rule describes regiochemistry in which the substitute bonds to fewer carbon substitutes. This is particularly true in the case of alkene or alkyne reactions, when carbocations usually generated tend to favor more substituted carbon, which is relatively uncommon. As a result of the substitution of carbocation, there is more hyperconjugation and induction, which increases the stability of the carbohydrate and makes it less unstable. ‘Addition of Hydrogen Bromide to Allyl Bromide’, a study published in 1933 by Morris Selig Karasch, was the first paper to explain this mechanism. HBr Radical Addition and Hydroboration-Oxidation are two examples of Anti-Markovnikov rule in action. 1 Unpaired electrons are present in every chemical compound that is classified as free radical.
Conclusion
Asymmetric alkenes are subjected to the rule, which states that when a protic acid HX or other polar reagent is added to them, the acid hydrogen (H) or electropositive part attaches to the carbon with more hydrogen substituents, and the halide (X) group or electronegative part attaches to the carbon with more alkyl substituents. Alternatively, in Markovnikov’s original definition, the rule is worded as follows: the X component must be added to the carbon containing the fewest hydrogen atoms whereas the hydrogen atom must be added to the carbon containing the highest amount of hydrogen atoms. Similarly, when an alkene combines with water in an additional reaction to generate an alcohol, which involves the production of carbocations, the result is the same. The hydroxyl group (OH) bonds to the carbon atom that has the greatest number of carbon–carbon bonds, whereas the hydrogen atom bonds to the carbon atom on the other end of the double bond that has the greatest number of carbon–hydrogen bonds.
