Which of the following compound will give three alkenes after dehydrohalogenation.

Options

A. `CH_3-CH_2-CH_2-CH_2-Br`
B. `CH_3-CH_2-undersetunderset(Br)(|)CH-CH_3`
C. `CH_3-undersetunderset(Br)(|)oversetoverset(CH_3)(|)C-CH_3`
D. `CH_3-CH_2-undersetunderset(Br)(|)CH-Ph`

Answer

To determine which compound will give three alkenes after dehydrohalogenation, we need to analyze each option provided. Dehydrohalogenation is an elimination reaction where a hydrogen atom and a halogen atom are removed from adjacent carbon atoms, resulting in the formation of a double bond (alkene).

### Step-by-Step Solution:

1. **Identify the Compounds:**
We need to analyze the given compounds one by one. Let's denote the compounds as follows:
- Compound A: CH3-CH2-CH2-CH2-Br
- Compound B: CH3-CH-Br-CH3
- Compound C: CH3-CH(CH3)-CH3-Br
- Compound D: CH3-CH2-CH-Br-Ph

2. **Analyze Compound A (CH3-CH2-CH2-CH2-Br):**
- This compound has only one beta carbon (the carbon adjacent to the carbon bonded to the bromine).
- Upon dehydrohalogenation, we can only remove a hydrogen from this single beta carbon.
- Resulting alkene: CH3-CH2-CH=CH2 (only one alkene).
- **Conclusion:** Only 1 alkene is formed.

3. **Analyze Compound B (CH3-CH-Br-CH3):**
- This compound has two beta carbons (the two adjacent carbons to the carbon bonded to bromine).
- Dehydrohalogenation can occur from either beta carbon.
- Possible alkenes:
- If hydrogen is removed from the left beta carbon: CH3-CH=CH-CH3 (cis and trans configurations possible).
- If hydrogen is removed from the right beta carbon: CH3-CH2-CH=CH2 (another configuration).
- **Conclusion:** A total of 3 alkenes can be formed (considering cis and trans).

4. **Analyze Compound C (CH3-CH(CH3)-CH3-Br):**
- This compound also has two beta carbons.
- However, both beta carbons are equivalent due to symmetry.
- Dehydrohalogenation will yield the same alkene regardless of which beta carbon is chosen.
- Resulting alkene: CH2=CH-CH3 (only one alkene).
- **Conclusion:** Only 1 alkene is formed.

5. **Analyze Compound D (CH3-CH2-CH-Br-Ph):**
- This compound has one beta carbon adjacent to the bromine.
- Dehydrohalogenation will yield one alkene with two different groups on the double bond.
- Resulting alkenes can be:
- If hydrogen is removed from the beta carbon: CH=CH-Ph (two configurations possible).
- **Conclusion:** A total of 2 alkenes can be formed.

### Final Conclusion:
After analyzing all the compounds, **Compound B (CH3-CH-Br-CH3)** is the only compound that can yield three distinct alkenes after dehydrohalogenation.