Question

Explain Markow nikoff’s rule with suitable example.

Answer 1

“When an unsymmetrical alkene reacts with hydrogen halide, the hydrogen adds to the carbon that has more number of hydrogen and halogen add to the carbon having fewer hydrogen”. This rule can also be stated as in the addition reaction of alkene/alkyne, the most electro negative part of the reagent adds on to the least hydrogen attached doubly bonded carbon.

Addition of water: (Hydration of alkenes)
Normally, water does not react with alkenes. In the presence of concentrated sulphuric acid, alkenes react with water to form alcohols. This reaction follows carbocation mechanism and Markovnikoff’s rule.

\[\begin{array}{cc}\phantom{...........................}\ce{OH}\\
\phantom{.........................}|\\
\ce{CH3 - C = CH2 ->[H+/H2O] CH3 - C - CH3}\\|\phantom{........................}|\\
\phantom{...}\ce{\underset{\text{2-methylpropene}}{CH3}}\phantom{.............}\ce{\underset{\text{2-methyl-2-proponal}}{CH3}}
\end{array}\]