which alkene does not follow Anti-Markownikoff's addition rule

Options

A. 2 - butene
B. 1 - butene
C. 2 - pentene
D. 2 - hexene

Answer

To determine which alkene does not follow the Anti-Markovnikov's addition rule, we need to analyze the given options based on their structures. The Anti-Markovnikov addition rule applies to unsymmetrical alkenes, where the addition of HX (where X is a halogen) occurs in such a way that the hydrogen atom attaches to the carbon with more hydrogen atoms, and the halogen attaches to the carbon with fewer hydrogen atoms.

### Step-by-Step Solution:

1. **Identify the Options**: We are given four options (A, B, C, D) which represent different alkenes. We need to analyze each one to see if it is symmetrical or unsymmetrical.

2. **Analyze 2-Butene (Option A)**:
- Structure: CH3-CH=CH-CH3
- This alkene is symmetrical because both sides of the double bond are identical (both sides have CH3 groups).
- Conclusion: 2-butene does not follow the Anti-Markovnikov addition rule.

3. **Analyze 1-Butene (Option B)**:
- Structure: CH2=CH-CH2-CH3
- This alkene is unsymmetrical because the two carbons involved in the double bond have different substituents (one has two hydrogens and the other has one hydrogen and a CH2 group).
- Conclusion: 1-butene follows the Anti-Markovnikov addition rule.

4. **Analyze 2-Pentene (Option C)**:
- Structure: CH3-CH=CH-CH2-CH3
- This alkene is also unsymmetrical because the two carbons in the double bond have different substituents.
- Conclusion: 2-pentene follows the Anti-Markovnikov addition rule.

5. **Analyze 2-Hexene (Option D)**:
- Structure: CH3-CH=CH-CH2-CH2-CH3
- This alkene is unsymmetrical as well, with different substituents on the double bond.
- Conclusion: 2-hexene follows the Anti-Markovnikov addition rule.

### Final Conclusion:
The alkene that does not follow the Anti-Markovnikov addition rule is **2-butene (Option A)**, as it is symmetrical.