1. Markownikoff’s Rule

2. Markownikoff’s Rule
“When a hydrogen halide reacts with an unsymmetrical alkene the hydrogen of the hydrogen halide attaches itself to the carbon of the alkene bearing the larger number of hydrogens and smaller number of carbons"

3. Addition reactions of unsymmetrical alkenes
Addition of HBr to propene CH3CH=CH2:
H–Br can add in two different ways
Two products are possible:
Contains more H atoms
CH3CH=CH2
CH3CH=CH2
H–Br
Br–H
CH3CH2–CH2Br
CH3CHBr–CH3
Minor product
Major product

4. It’s all controlled by carbocations
Secondary carbocation
Two C joined to C+
Primary carbocation
One C joined to C+
Major product
Minor product

5. Types of carbocation Least Primary carbocation stable
One carbon chains attached to C+
Secondary carbocation:
Two carbon chains attached to C+
Tertiary carbocation:
Three carbon chains attached to C+
Most
stable

6. Reasons for carbocation stability
Least
stable
Electron-donating ability of alkyl groups.
Each alkyl group pushes electrons towards C+ charge of carbocation.
Positive charge is spread over alkyl groups
The more alkyl groups attached to the C+
The more the positive charge is spread out
The greater the stability of the carbocation
Primary
Secondary
Most
stable
Tertiary