Which of the following react with `HBr` at faster rate ?

Options

A.
B.
C.
D.

Answer

To determine which of the given compounds reacts with HBr at a faster rate, we need to analyze the stability of the carbocations formed during the reaction. The reaction mechanism involves the following steps:

### Step-by-Step Solution:

1. **Understanding the Reaction**:
The reaction of an alcohol (ROH) with HBr involves the protonation of the hydroxyl group (OH) to form a better leaving group (water, H2O).

2. **Formation of Carbocation**:
- When HBr reacts with ROH, the OH group gets protonated, forming ROH2⁺.
- The water molecule (H2O) then leaves, resulting in the formation of a carbocation (R⁺).

3. **Stability of Carbocations**:
- The stability of the carbocation is crucial for the reaction rate. The order of carbocation stability is:
- Tertiary (3°) > Secondary (2°) > Primary (1°) > Methyl (0°).
- Tertiary carbocations are stabilized by the inductive effect of surrounding alkyl groups.

4. **Analyzing the Given Options**:
- For each compound provided in the options, identify the type of carbocation that would form upon reaction with HBr.
- Determine whether it is a primary, secondary, or tertiary carbocation.

5. **Comparing the Stability**:
- The compound that forms a tertiary carbocation will react the fastest with HBr because it is the most stable.
- If multiple compounds form secondary carbocations, compare their structures to determine which one is more stable based on the number of alkyl groups attached.

6. **Conclusion**:
- Identify the compound that forms the most stable carbocation (tertiary) and conclude that this compound will react with HBr at the fastest rate.

### Final Answer:
The compound that forms a tertiary carbocation will react with HBr at a faster rate.