The rule states that when adding a protinic acid HX or other polar reagent to an asymmetric alkene, the acidic acid hydrogen (H) or electropositive part with more hydrogen substituents is bound to carbon and the halide group (X) or electronegative part is bound to carbon with more alkyl substituents. This contrasts with Markovnikov`s original definition, which states that component X is added to carbon with the fewest hydrogen atoms, while the hydrogen atom is added to carbon with the largest number of hydrogen atoms. [4] We use chemical reactions to synthesize chemical compounds. If we have the required quantities of reagents and catalysts, we can obtain the desired product by providing other conditions such as the right temperature. But sometimes the chemical reaction may not give the desired compound or result in a mixture of products composed of the desired product, as well as other products. This situation can be explained by the Markovnikov rule. Markovnikov`s rule explains why a particular atom or group is bound to a particular carbon atom rather than another carbon atom in the same molecule. The anti-Markovnikov rule explains the opposite situation of the Markovnikov rule. The main difference between markovnikov`s rule and the anti-Markovnikov rule is that Markovnikov`s rule states that hydrogen atoms are bonded to the carbon atom in an addition reaction with more hydrogen substitutes, while the anti-Markovnikov rule states that hydrogen atoms are bonded to the carbon atom with the fewest hydrogen substitutes. In the presence of peroxides, H adds a smaller number of H atoms to the C atom. This is the anti-Markovnikov additive. The resulting product is 1-bromopropane.

1. “Regioselectiveness”. Illustrated Glossary of Organic Chemistry – Regioselective; Regiochemistry, Available here. Accessed September 12, 2017.2. “Markovnikov`s rule”. Wikipedia, Wikimedia Foundation, August 31, 2017, available here. Retrieved 12 September 2017. Given their lack of carbocation intermediates or the fact that we add the same to the two carbons of the old Pi bond. You should always consider syn/anti-addition, which is the third and final hydration reaction of the alkene. And the only one that adds anti-Markovnikov. I`ve heard that this rule has been “memorized” after some of the following mnemonics: See what happens when we predict the product for hydrohalogination when we use the “add nucleophilic to more substituted carbon” rule vs.” add nucleophilic to the most stable carbocation position”.

The anti-Markovnikov rule can be illustrated by adding 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 additives. Early chemists discovered that the reason for the variability in the ratio between Markovnikov and anti-Markovnikov reaction products was due to the unexpected presence of radical ionizing substances such as peroxides. The explanation is that the O-O bond in peroxides is relatively weak. With the help of light, heat or sometimes even acting alone, the O-O bond can divide to form 2 radicals. Radical groups can then interact with HBr to create a Br radical, which then reacts with the double bond. Because the bromine atom is relatively large, it is more likely to strike and react with the least substituted carbon, as this interaction creates fewer static interactions between the carbon and the bromine radical. In addition, the radical species, similar to a positively charged species, is more stable when the unpaired electron is in the most substituted position. The radical intermediate is stabilized by hyperconjugation. In the more substituted position, more carbon-hydrogen bonds are aligned with the electron-poor molecular orbital of the radical.

This means that there are more hyperconjugation effects, so the position is more favorable. [5] In this case, final carbon is a reagent that produces a primary addition product instead of a secondary addition product. Syn and anti-addition refer to which face will add AU Pi linking the two groups. To demonstrate the example of the anti-Markovnikov rule of regiochemistry, we use 2-methylpropene as an example below. Reactions to the addition of free radicals do not obey Markovnikov`s rule, since the regioselectivity of the mechanisms of these reactions is not predicted by Markovnikov`s rule. These reactions are usually referred to as anti-Markovnikov addition reactions. 1. “Markovnikov Rule” (CC BY-SA 3.0) via Wikimedia Commons2. “Markovnikov and the anti-Mark addition” By 5402013SD – Own work (CC BY-SA 3.0) via Commons Wikimedia So we understand how Markovnikov`s rule is influenced by carbokation intermediaries and we know what reactions follow the addition of Markovnikov or the addition anti-Markovnikov. The anti-Markovnikov rule defines regiochemistry, in which the substituent is bound to a less substituted carbon instead of the more substituted carbon. Indeed, substituted carbocation allows more hyperconjugation and induction, which results in a more stable carbocation.

Mark refers to Markovnikov`s rule, while Anti-Mark refers to the addition Anti-Markovnikov. Also called the Kharasch effect (named after Morris S. Kharasch), these reactions, which do not involve a carbocation intermediate, can react by other mechanisms that have regioselectivities not dictated by Markovnikov`s rule, such as the addition of free radicals.