Question

Explain anti-Markovnikov's rule.

Answer 1

Anti Markovnikov Rule

• The Anti Markovnikov rule indicates that hydrogen atoms are attached to the carbon atom with the least hydrogen substituents.
• Anti-Markovnikov rule explains the Regio chemistry where the substituent is bonded to a less substituted carbon, rather than the more substituted carbon.
• This process is opposite to the Markovnikov rule.
• In Anti markovnikov rule, is applied in the presence of peroxide.

Steps involved is given below:

• Step 1: Addition of Bromine ion

Bromine is added to $1^o$ carbanion in the presence of peroxide for stability

$\underset{\mathrm{Bromine}\mathrm{ion}}{{\mathrm{Br}}^{-}}+\underset{\mathrm{Propene}}{{\mathrm{CH}}_2={\mathrm{CH}}_2-{\mathrm{CH}}_3}{\to }^{{\mathrm{H}}_2{\mathrm{O}}_2}\underset{1-\mathrm{Bromo}\mathrm{Propane}\mathrm{ion}}{\mathrm{Br}-{\mathrm{CH}}_2-{\mathrm{CH}}^{-}-{\mathrm{CH}}_3}$

• Step 2: $2^o$Reaction of carbanion with hydrogen bromide

$\underset{1-\mathrm{Bromo}\mathrm{Propane}\mathrm{ion}}{\mathrm{Br}-{\mathrm{CH}}_2-{\mathrm{CH}}^{-}-{\mathrm{CH}}_3}+\underset{\mathrm{Hydrogen}\mathrm{bromide}}{\mathrm{HBr}}\to \underset{1-\mathrm{Bromo}\mathrm{propane}}{{\mathrm{BrCH}}_2-{\mathrm{CH}}_2-{\mathrm{CH}}_3}+\underset{\mathrm{Bromine}\mathrm{anion}}{{\mathrm{Br}}^{-}}$

Thus, in the Anti Markovnikov rule substituent hydrogen is added to less substituted carbon.