The given reaction is `CH_3-CH=CH-CH_2OHoverset(HBr)rarrCH_3-overset(Br)overset(|)(CH)-CH=CH_2`

Options

A. E1
B. `S_N1`
C. `S_N2`
D. E2

Answer

To solve the given reaction step by step, we will analyze the reaction of 2-buten-1-ol (CH3-CH=CH-CH2OH) with HBr and determine the mechanism involved.

### Step-by-Step Solution:

1. **Identify the Reactant and the Reaction**:
The reactant is 2-buten-1-ol (CH3-CH=CH-CH2OH). When treated with HBr, we need to consider how the components will interact.

**Hint**: Look for functional groups in the reactant that can interact with HBr.

2. **Protonation of the Alcohol**:
The hydroxyl group (-OH) of the alcohol can act as a base and will accept a proton (H+) from HBr. This forms a protonated alcohol (CH3-CH=CH-CH2OH2+), which is more reactive.

**Hint**: Remember that alcohols can be converted into better leaving groups by protonation.

3. **Formation of a Carbocation**:
The protonated alcohol is unstable and will lose a water molecule (H2O) to form a carbocation. In this case, the carbocation formed is a secondary carbocation (CH3-CH=CH-CH2+).

**Hint**: Identify the type of carbocation formed (primary, secondary, or tertiary) as it affects stability.

4. **Carbocation Rearrangement (if applicable)**:
In this case, the secondary carbocation is stable, and there is no rearrangement needed. The stability of the carbocation will dictate the next step.

**Hint**: Consider if the carbocation can rearrange to a more stable form.

5. **Nucleophilic Attack by Bromide Ion**:
The bromide ion (Br-) from HBr will attack the carbocation. Since the carbocation is secondary, the Br- will attach to the positively charged carbon, leading to the formation of the product.

**Hint**: Nucleophiles attack positively charged centers; identify where the Br- will bond.

6. **Final Product**:
The final product of this reaction is 3-bromobutene (CH3-CH(Br)-CH=CH2), where Br has substituted the position of the hydroxyl group.

**Hint**: Ensure you keep track of where each atom goes during the reaction.

### Summary:
The overall reaction involves the protonation of the alcohol, formation of a stable secondary carbocation, followed by nucleophilic attack by Br-. This is characteristic of an SN1 reaction mechanism.

### Final Answer:
The reaction proceeds via an SN1 mechanism, resulting in the formation of 3-bromobutene.