Markovnikov Rule, what is Markovnikov Rule?

In organic chemistry, the Mahalobis rule (also known as Markovnikov's rule, Markovnikov's rule, or Markonikov's rule) is a regioselective empirical rule based on Zaitsev's rule, which states that when an electrophilic addition reaction (e.g., hydrogen halide and olefin) occurs, the electrophile in the electrophile (e.g., hydrogen) is always added to the carbon atom with the most hydrogen (e.g., substitution). Negative groups, such as halogens, are added to the carbon atom with the least amount of hydrogen (the most substitution).

Brief introduction. The Markovnikov Rule is simply known as the Markov Rule. It refers to a law in organic reactions.

Discovered in 1870 by Markovnikov. The Mahalanobis rule states that in the electrophilic addition reaction of an olefin, the positive group of the addition reagent will be added to the carbon atom with fewer substituents (or more hydrogen) in the olefin double bond (or triple bond).

It illustrates why only one of the two isomers is often produced in the reaction of an addition reagent with an olefin, if it is possible. For example, in the addition reaction of hydrogen halide to isobutylene, the cation H of Hx is attached to the carbon atom at the end of the double bond to form an tertiary halide:

This selective addition to the Marhalanobis rule is called location selection and can be illustrated by the electronic effect. The positively charged part of the Y attacks the double bond first, and it tends to add to the end of the double bond with the higher electron density, while the resulting carbocation has a substituent at the end

Due to the superconjugated stabilization of alkyl groups, which is conducive to the dispersion of positive charge, the structural formula A is more stable than B, which is the main direction of addition reaction. Therefore, the Marhalanobis rule can be used to predict the direction of the electrophilic addition reaction. The Marhalanobis rule can be formulated in another way:

When asymmetric olefins are added to polar reagents, the positive ions or partially positively charged parts of the reagent are added to the partially negatively charged carbon atoms in the heavy bonds, and the negative ions or partially negatively charged parts of the reagents are added to the partially positively charged carbon atoms in the heavy bonds. This applies not only to addition reagents that do not contain hydrogen atoms, but also to derivatives of unsaturated hydrocarbons containing absorbent groups in the molecule.

In radical addition reactions, the addition position of the addition reagent to the olefin is often inconsistent with the Marhalanobis rule. For example, in the addition reaction of hydrogen bromide to isobutylene, if the homemade peroxide is presented, the bromine atom is attached to the terminal carbon atom instead of to the second carbon atom as foreshadowed by the Marhalobis rule, resulting in 2-methylbromopropane:

This phenomenon is called the peroxide effect. The reason for this phenomenon is that in the radical addition reaction described above, the reagent that first attacks the double bond is br·.

Due to the different stability of free radical generation, the secondary carbon free gene is stabilized by the superconjugation of two methyl groups, which is greater than that of the primary carbon radical, so the former becomes the main direction of addition reaction.

The Markovnikov rule, also known as the Markovnikov bonus. Namely"Alkene.

With the addition of hydrohalic acid, hydrogen is added to the carbon with more hydrogen".The Marshalls rule appears.

The reason for this is that the more substituents, the more stable and easier the carbocation is to form. In this way, the dominant substituent carbon is preferentially replaced by negative ions.

Attack bonus. In the electrophilic addition reaction of alkenes, the hydrogen cation first attacks the double bond (this step is a constant velocity step) to form a carbocation, and then the halogen anion attacks the carboanion to form the product. Stereochemical studies have found that the subsequent attack of halogen anion occurs from the opposite direction of hydrogen ions, that is, trans addition.

For example, the addition of propylene and HBR: CH-CH=CH+ HBR CH-CHBR-CH In the first step, HBR ionization generates H and BR ions, and hydrogen ions are used as electrophiles to attack C=C double bonds first, forming such a structure. In the second step, since hydrogen has already taken a position on one side, bromine can only attack from the other side.

According to the Marhalanobis rule, bromine bonds with 2-carbon, and then hydrogen hits the side of 1-carbon, and the reaction is complete. Water, sulfuric acid, hypohaloic acid, etc. can all be electrophilic, and their addition is a Marhalanobis addition, that is, they all conform to the Markov rule.

First of all, this rule is only a summary of experience, and it is actually divided into Marhalanis and anti-Marben according to the stability of the intermediates. The following is an introduction to the Marshalls Rule.

In organic chemistry, the Mahalobis rule (also known as Markovnikov's rule, Markovnikov's rule, or Markonikov's rule) is a regioselective empirical rule based on Zaitsev's rule, which states that when an electrophilic addition reaction (e.g., hydrogen halide and olefin) occurs, the electrophile in the electrophile (e.g., hydrogen) is always added to the carbon atom with the most hydrogen (e.g., substitution). Negative groups, such as halogens, are added to the carbon atom with the least amount of hydrogen (the most substitution).

The reason for the Marhalanobis rule is the formation of relatively stable carbocations in the electrophilic addition reaction. The addition of a carbon atom with H+ causes a positive charge to be introduced on the other carbon atoms, forming a carbocation. Due to the induction effect and the superconjugation effect, the more substituents (carbon or electron-donor groups attached to the carbon) are the more stable carbocations with the Malcolis rule.

The main product of the addition reaction is produced by a more stable intermediate. Therefore, when the olefin is added to hydrogen bromide, the hydrogen in hydrogen bromide is always added to the carbon with the most hydrogen, and the halogen group is added to the carbon with the least hydrogen. However, other less stable carbocations remain, and the products produced through them are not Marhalanobis rules and are usually by-products of the reaction.

This rule can be summarized as "hydrogen for more hydrogenation" or "the rich get richer and the poor get poorer": more hydrogen gets more hydrogen, and less hydrogen gets additional substituents. The same is true for other asymmetric electrophiles.

The positive electric group is added to the less substituted carbon, and the negative group is added to the carbon that is more replaced.