Question

When is Markonikov’s rule valid?

Answer 1

Alkenes are unsaturated hydrocarbons consisting of double bonded carbon-carbon atoms. Due to the presence of double bonds, alkanes undergo additional reactions. When an unsymmetrical alkene is treated with the reagents like hydrochloric acid or hydrogen bromide the reaction takes place according to Markonikov’s rule.

Complete answer:
Chemical compounds are classified into different functional groups based on the group present in them. The compounds containing only carbon and hydrogen atoms are known as hydrocarbons. Alkanes, alkenes and alkynes are hydrocarbons. Alkenes are unsaturated hydrocarbons consisting of double bonded carbon-carbon atoms. Due to the presence of double bond, alkenes undergo additional reactions when treated with the reagents like hydrochloric acid or hydrogen bromide which consisting of both negative and positive parts.
When unsymmetrical alkenes are treated with the reagents like hydrochloric acid or hydrogen bromide the reaction takes place according to Markonikov’s rule.
Markonikov’s rule states that the negative part of the reagent should attack on the carbon containing less number of hydrogen atoms and the positive part of the reagent attacks on the carbon containing more number of hydrogen atoms.
The chemical reaction that follows Markonikov’s rule is
$C{H_3}C{H_2}CH = C{H_2} + HBr \to C{H_3}C{H_2}CH\left( {Br} \right) - C{H_3}$
Thus, Markonikov’s rule is followed in the addition reaction of unsymmetrical alkenes.

Note:
In presence of peroxides, anti- Markonikov’s rule is followed, which states that the negative part of the reagent should attacks on the carbon containing more number of hydrogen atoms and the positive part of the reagent attacks on the carbon containing less number of hydrogen atoms. Anti- Markonikov’s rule is exactly opposite to Markonikov’s rule.