The one giving maximum number of isomeric alkenes on dehydrohalogenation reaction is (excluding rearrangement)

Options

A. 2-Bromopentane
B. 1-Bromo-2-methylbutane
C. 2-Bromopropane
D. 2-Bromo-3,3-dimethylpentane

Answer

To solve the problem of determining which compound gives the maximum number of isomeric alkenes upon dehydrohalogenation, we will analyze the options provided. The focus will be on the structure of the compounds and the potential alkenes that can be formed from them.

### Step-by-Step Solution:

1. **Identify the Compounds**: The question likely presents several compounds, but we will focus on the example given in the transcript, which is 2-bromopentane.

2. **Understand Dehydrohalogenation**: Dehydrohalogenation is a reaction where a hydrogen halide (HX) is removed from an alkyl halide, resulting in the formation of an alkene. The general reaction can be represented as:
\[ R-CHBr-CH_2-CH_2-R' \rightarrow R-CH=CH-CH_2-R' + HBr \]

3. **Draw the Structure of 2-Bromopentane**: The structure of 2-bromopentane is:
\[ CH_3-CHBr-CH_2-CH_2-CH_3 \]
This compound has a bromine atom on the second carbon of a five-carbon chain.

4. **Determine Possible Alkenes**: Upon dehydrohalogenation of 2-bromopentane, we can form different alkenes:
- **1-Pentene**: Formed by removing H from the first carbon and Br from the second carbon.
- **2-Pentene**: Formed by removing H from the second carbon and Br from the second carbon. This can exist as:
- **Cis-2-pentene**
- **Trans-2-pentene**

5. **Count the Isomers**: From the above analysis, we can summarize the possible alkenes:
- 1-Pentene (1 isomer)
- Cis-2-pentene (1 isomer)
- Trans-2-pentene (1 isomer)

Thus, the total number of isomeric alkenes formed from 2-bromopentane is 3.

6. **Compare with Other Compounds**: If we were to analyze other compounds like 1-bromobutane or 2-bromopropane:
- **1-Bromobutane**: Would only yield 1-butene (1 isomer).
- **2-Bromopropane**: Would yield only propene (1 isomer).

7. **Conclusion**: After comparing the number of isomeric alkenes formed from various alkyl halides, it is clear that 2-bromopentane gives the maximum number of isomeric alkenes (3).

### Final Answer:
The compound that gives the maximum number of isomeric alkenes on dehydrohalogenation is **2-bromopentane**.