Which of the following can’t be an example of an `S_(N)`2 reaction?

Options

A. `CH_(3)- CH_(2) - OH overset(-H_(2)O)(rarr) CH_(2) = CH_(2)`
B. `(CH_(3))_(2) "CHBr" overset(OH^(-))(rarr) (CH_(3))_(2) CH - OH + Br^(-)`
C. `CH_(3) Br overset(OH^(-))(rarr) CH_(3)OH + Br^(-)`
D. `(CH_(3))_(3) C - Br overset(OH^(-))(rarr)(CH_(3))_(3) C-OH + Br^(-)`

Answer

To determine which of the given options cannot be an example of an SN2 reaction, we first need to understand the characteristics of SN2 reactions.

### Step-by-Step Solution:

1. **Understanding SN2 Reactions**:
- SN2 stands for bimolecular nucleophilic substitution.
- It is a second-order reaction where the rate depends on the concentration of both the substrate (haloalkane) and the nucleophile.
- SN2 reactions occur in a single step, involving a transition state where the nucleophile attacks the substrate and the leaving group departs simultaneously.
- SN2 reactions typically involve primary or secondary haloalkanes, as steric hindrance can prevent the nucleophile from effectively attacking tertiary haloalkanes.

2. **Analyzing the Options**:
- We need to evaluate each option to see if it fits the criteria for an SN2 reaction.

3. **Option 1**:
- If this option leads to the formation of an alkene, it typically involves elimination rather than substitution. Therefore, it cannot be an SN2 reaction.

4. **Option 2**:
- If this option results in the formation of an alcohol from a primary haloalkane, this is a classic example of an SN2 reaction.

5. **Option 3**:
- Similar to option 2, if this option also results in the formation of an alcohol from a primary haloalkane, it is also an example of an SN2 reaction.

6. **Option 4**:
- If this option leads to the formation of a tertiary alcohol from a tertiary haloalkane, it would not be an SN2 reaction. Tertiary substrates typically undergo SN1 reactions due to steric hindrance.

7. **Conclusion**:
- Based on the analysis, options 1 and 4 cannot be examples of SN2 reactions. Option 1 involves elimination (alkene formation), and option 4 involves a tertiary substrate leading to an SN1 reaction.

### Final Answer:
Options 1 and 4 cannot be examples of an SN2 reaction.