Which of the following reaction occur most rapidly ?

Options

A. `(CH_(3))_(2)CHOHoverset(HBr)(to)`
B. `(CH_(3))_(2)CHOHoverset(HI)(to)`
C. `(CH_(3))_(3)C-OHoverset(HBr)(to)`
D. `(CH_(3))_(3)C-OHoverset(HI)(to)`

Answer

To determine which of the following reactions occurs most rapidly, we need to analyze the reactivity of the compounds involved in each reaction. The key factors that influence the rate of reaction include the nature of the reactants (e.g., alcohols and halogens) and their degree of substitution.

### Step-by-Step Solution:

1. **Identify the Reactants**:
- We have reactions involving alcohols and halogens (specifically HI and HBr).

2. **Understand the Reactivity of Halogens**:
- Among the halogens, HI is more reactive than HBr. This means that reactions involving HI will generally occur more rapidly than those involving HBr.

3. **Assess the Alcohols**:
- The reactivity of alcohols depends on their degree of substitution:
- Tertiary alcohols (3°) react faster than secondary alcohols (2°), which in turn react faster than primary alcohols (1°).

4. **Compare the Given Reactions**:
- If we have two reactions with HBr (let's say Reaction 1 and Reaction 3) and two reactions with HI (Reaction 2 and Reaction 4), we can conclude that:
- Reactions with HI will be faster than those with HBr.
- Among the reactions with HI, the tertiary alcohol will react faster than the secondary alcohol.

5. **Rank the Reactions**:
- For the reactions involving HBr (1 and 3), the one with the tertiary alcohol will be faster than the one with the secondary alcohol.
- For the reactions involving HI (2 and 4), the one with the tertiary alcohol will be the fastest.

6. **Conclusion**:
- Based on the analysis, Reaction 4 (which involves HI and a tertiary alcohol) will occur most rapidly.

### Final Answer:
The reaction that occurs most rapidly is **Option 4**.