Which is incorrect about alkyl bromide having molecular formula `C_5H_11Br`

Options

A. Only one isomeric alkyl bromide undergoes E1 elimination at the fastest rate
B. Only one is incapable of reacting by the E2 mechanism
C. Only one isomer gives a single alkene on E2 elimination
D. 2-Bromopentane gives the most complex mixture of alkenes on E2 elimination

Explanation

To determine which statement is incorrect about the alkyl bromide with the molecular formula C5H11Br, we will analyze the provided options step by step.

### Step 1: Identify the Isomers
The molecular formula C5H11Br indicates that there are several possible structural isomers. In total, there are eight isomers of C5H11Br. These isomers can be categorized based on the position of the bromine atom and the arrangement of carbon atoms.

**Hint:** Consider the different structural arrangements of carbon atoms and the position of the bromine atom to identify the isomers.

### Step 2: Analyze Each Statement
Now, we will evaluate each statement provided in the question.

1. **Statement 1:** "Only one isomeric alkyl bromide undergoes elimination at the fastest rate."
- This statement is incorrect. There are multiple isomers, and more than one can undergo elimination reactions at significant rates.

**Hint:** Think about the factors that influence the rate of elimination reactions, such as sterics and the stability of the resulting alkene.

2. **Statement 2:** "Only one is incapable of reacting by the E2 mechanism."
- This statement is correct. In general, certain sterically hindered isomers may not favor the E2 mechanism due to the requirement for a specific alignment of the leaving group and the hydrogen atom being eliminated.

**Hint:** Recall the requirements for the E2 mechanism and how steric hindrance can affect reactivity.

3. **Statement 3:** "Only one isomer gives a single alkene on E2 elimination."
- This statement is also correct. Some isomers can lead to multiple products upon elimination, while others may yield a single product.

**Hint:** Consider how the structure of the alkyl bromide influences the number of possible alkene products.

4. **Statement 4:** "2-bromo pentane gives the most complex mixture of alkenes on E2 elimination."
- This statement is correct. 2-bromo pentane can lead to multiple alkenes due to different elimination pathways.

**Hint:** Think about how branching and the position of the bromine can lead to various elimination products.

### Step 3: Conclusion
After analyzing the statements, we conclude that the first statement is the incorrect one.

**Final Answer:** The incorrect statement is: "Only one isomeric alkyl bromide undergoes elimination at the fastest rate."