Rule Markovnikova V. V. Essence and examples

In chemical reactions at the place of destruction of the double bond in alkenes and triple in alkynes, different particles can be attached. What are the laws of this process? The behavior of asymmetric homologues of ethylene during hydrohalogenation and hydration was studied by the Russian scientist VV Markovnikov. He found that the mechanism of the reaction depends on how much hydrogen is bound to the carbon in the double bond. The hypothesis advanced by the scientist was confirmed after discoveries in the field of the structure of the atom. The Markovnikov rule laid the foundation for the creation of a scientific theory that has practical application. It allows more rationally organize the production of polymers, lubricants, alcohols.

The Markovnikov Rule

The Russian scientist devoted much time in his work to studying the mechanism of attaching asymmetric reagents to unsaturated hydrocarbons. In his article published in German in 1870, VV Markovnikov drew the attention of the scientific community to the selectivity of the interaction of hydrogen halides with carbon atoms that are located in a double bond in unsymmetrical alkenes. The Russian researcher cited the data that he had obtained empirically in his laboratory. Markovnikov wrote that halogen necessarily joins the carbon atom, which contains the least amount of hydrogen atoms. A great popularity of the work of the scientist was acquired at the beginning of the 20th century. The hypothesis of the interaction mechanism proposed by him was called the "Markovnikov rule".

Life and work of an organic scientist

Vladimir Vasil'evich Markovnikov was born on December 25, 1837 (in style according to the style of St. Petersburg). He studied at the University of Kazan, later taught at this school and at Moscow University. Markovnikov studied the behavior of unsaturated hydrocarbons in interaction with hydrogen halides since 1864. Until 1899, scientists from other countries did not attach importance to the conclusions of the Russian chemist. Markovnikov, in addition to the rule, named in his honor, made a number of other discoveries:

• Received cyclobutanedicarboxylic acid;
• Investigated the oil of the Caucasus and discovered in it organic substances of a special composition - naphthenes;
• Established the difference in the melting temperatures of compounds with branched and rectilinear chains;
• Proved the isomerism of fatty acids.

The works of the scientist greatly contributed to the development of domestic chemical science and industry.

The essence of the hypothesis put forward by Markovnikov

The scientist devoted many years to the study of the reactions of addition of reagents to unsaturated hydrocarbons with one double bond (alkenes). He noted that if hydrogen is present in the compounds, then it is directed to that carbon atom, which contains more particles of this kind. Anion joins the adjacent carbon. This is Markovnikov's rule, its essence. The scientist brilliantly predicted the behavior of particles, the structure of which at that time still had not very clear ideas. In accordance with the rule, complex substances having the composition of HX are added to the ethylene hydrocarbons, where X:

• halogen;
• Hydroxyl;
• Acidic residue of sulfuric acid;
• Other particles.

The modern sounding of the Markovnikov rule differs from that of the scientist: the hydrogen atom from the HX molecule attached by the alkene is directed to that carbon in a double bond that already contains more hydrogen, and the particle X is directed to the least hydrogenated atom.

The mechanism of attachment of electrophilic particles

Consider the types of chemical transformations in which the Markovnikov rule is applied. Examples:

1. The reaction of addition to propene hydrogen chloride. During the interaction between the particles, the double bond is destroyed. The chlorine anion is sent to the less hydrogenated carbon that was in the double bond. Hydrogen interacts with the most hydrogenated of these atoms. 2-chloro-propane forms.
2. In the addition reaction of the water molecule, hydroxyl from its composition is suitable for less hydrogenated carbon. Hydrogen is attached to the most hydrogenated atom with a double bond.

There are exceptions to the rule proposed by Markovnikov in those reactions where alkenes act as reagents, in which carbon in the double bond already has a number of electronegative groups. It partially selects the electron density to which positively charged hydrogen is usually attracted. The rule is also not observed in reactions that follow a radical, and not an electrophilic, mechanism (the Harish effect). These exceptions do not detract from the merits of the rule derived by the outstanding Russian organic chemist V. V. Markovnikov.