Difference Between Markovnikov Rule And Anti Markovnikov Rule

Markovnikov Rule

In organic chemistry, Markovnikov ‘s rule also referred to as Markownikoff’s rule describes the outcome of some addition reactions. The rule was formulated by Russian chemist Vladimir Markovnikov in 1870. The rule states that, with the addition of a Protic acid HX (X=Cl, Br, I) to an asymmetric alkene, the acid hydrogen (H) gets attached to the carbon with more hydrogen substituents and the halide (X) group gets attached to the carbon with more alkyl substituents. In other words, hydrogen is added to the carbon atom with more number of hydrogen atoms attached to it and halide is added to the carbon atom with least number of hydrogen atoms. An example of a reaction that observes Markovnikov’s rule is the addition of hydrobromic acid (HBr) to propene.

Markovnikov’s rule is also true when an alkene reacts with water in addition reaction to form an alcohol which involves formation of carbocations. The hydroxyl group (OH) bonds to the carbon that has the greater number of carbon-carbon bonds, while the hydrogen bonds to the carbon on the other end of the double bond which has more carbon-hydrogen bonds.

Applications of Markovnikov’s Rule

Halohydrin formation (in alcohol and water)
Acid catalyzed hydration
Oxynercurationand Demercuration

What You Need To Know About Markovnikov Rule

The Markovnikov rule states that in addition reactions of alkenes or alkynes, the proton is added to the carbon atom that has the greatest number of hydrogen atoms attached to it.
The mechanism of Markovnikov rule in chemistry is an ionic mechanism.
According to this rule, the hydrogen atom is attached to the carbon atom with the highest number of hydrogen substituent.
No medium is required in Markovnikov rule.
The electronegative part of the alkyl halide usually goes to the carbon which consists of the least number of hydrogen atoms attached to a carbon atom in Markovnikov rule.
In Markovnikov addition reaction, the carbocation, which is the intermediary in this reaction, then undergoes a rearrangement which increases the stability of carbocation.
HBr, HI, HCl and H₂O are the reactants that are used in Markovnikov rule.
In Markovnikov rule major product is given by HBr from (CH₃)2C=CHCH₃will produce (CH₃)2CBrCH₂CH₃
The hydrogen ion from the reactant HX in Markovnikov rule starts the attack on the carbon-carbon double bond.
The Markovnikov addition of hydrogen halide to olefin usually results in the production of carbocation as the reaction intermediary.

Anti-Markovnikov Rule

Anti Markovnikov addition also referred to as Kharasch effect is an example of addition reaction of alkenes which is an exception to the Markovnikov’s rule. It is one of the few reactions following free radical mechanism in organic chemistry in place of electrophilic addition as suggested by Markovnikov. This reaction is observed only with HBr, not with HCl or HI. In this process, a peroxide compound is used in the generation of free radicals.

Anti-Markovnikov’s rule describes the regiochemistry of mechanisms where the substituent is bonded to a less substituted carbon rather than the more substituted carbon. This process is quite unusual as carbocations which are commonly formed during alkene or alkyne reactions tend to favor the more substituted carbon. This is because substituted carbocation allow more hyperconjugation to happen, making carbocation more stable. The anti-markovnikov rule can be explained using the addition of hydrogen bromide to propene in the presence benzoyl peroxide.

Anti-Markovnikov behavior extends to more chemical reactions than additions to alkenes. Anti-Markovnikov behavior is observed in certain rearrangement reactions and in the hydration of phenylacetylene by auric catalysts which give acetophenone.

Applications Of Anti-Markovnikov’s Rule

Hydroboration-Oxidation
Radical Halogenation

What You Need To Know About Anti Markovnikov Rule

Anti Markovnikov rule states that in addition reactions of alkenes or alkynes, the proton is added to the carbon atom that has the least number of hydrogen atoms attached to it.
The mechanism of anti Markovnikov rule is a free radical mechanism.
According to Anti Markovnikov rule, the hydrogen atom is attached to the carbon atom with the least number of hydrogen substituent.
A medium is required for anti Markovnikov rule. The medium is generally Peroxide or ultraviolet.
The electronegative part of alkyl halide attaches to the carbon atom that consists of the highest number of hydrogen atoms attached to the carbon atom in anti Markovnikov rule.
In anti Markovnikov rule, the produced intermediary does not undergo rearrangement.
HBr is the only free reactant that is used in anti Markovnikov rule and HCl, or HI are not used in this kind of addition reaction.
In the presence of peroxide, the main product of anti Markovnikov rule will be given as (CH₃)2CHCH(Br)CH₃
Halogen-free radical X, which is formed by the communication between HX and the radical peroxide, usually starts the attack on carbon-carbon double bond in anti Markovnikov rule.
The creation of carbon-free radical is generally known as the reaction intermediary in anti Markovnikov rule.

Also Read: Difference Between Substitution Reaction And Addition Reaction