`CH_(3)-CH=CH-CH_(2)-CH_(3) overset(HI)to underset("major")A`
Compound A is

Options

A. `CH_(3)-CH_(2)-underset(|)underset(|)CH-CH_(2)-CH_(3)`
B. `CH_(3)-underset(|)underset(|)CH-CH_(2)-CH_(2)-CH_(3)`
C. `CH_(3)-underset(|)underset(|)overset(CH_(2))overset(|)C-CH_(2)-CH_(3)`
D. `CH_(3)-underset(CH_(3))underset(|)overset(CH_(3))overset(|)C-CH_(2)I`

Answer

To solve the question regarding the reaction of 1-pentene (CH₃-CH=CH-CH₂-CH₃) with hydroiodic acid (HI) to form compound A, we will follow these steps:

### Step 1: Identify the Structure of the Given Compound
The given compound is 1-pentene, which has the following structure:

```
CH₃
|
CH=CH
|
CH₂
|
CH₃
```

### Step 2: Apply Markovnikov's Rule
When HI adds to an alkene, it follows Markovnikov's rule, which states that the hydrogen atom (H) will attach to the carbon with the greater number of hydrogen atoms, while the iodine (I) will attach to the carbon with fewer hydrogen atoms.

### Step 3: Determine Possible Carbocation Intermediates
1. The double bond is between the second and third carbon atoms. When H⁺ adds to the second carbon (C-2), it will create a carbocation on the third carbon (C-3).
2. Alternatively, if H⁺ adds to the third carbon (C-3), it will create a carbocation on the second carbon (C-2).

### Step 4: Analyze the Stability of the Carbocations
1. **Carbocation at C-3**: This carbocation is a secondary carbocation, which is relatively stable due to the presence of two alkyl groups.
2. **Carbocation at C-2**: This carbocation is a primary carbocation, which is less stable compared to the secondary carbocation.

### Step 5: Consider the Attack of Iodide Ion (I⁻)
The iodide ion (I⁻) will attack the more stable carbocation. Since the secondary carbocation at C-3 is more stable, the I⁻ will preferentially attack this position.

### Step 6: Draw the Final Product
When I⁻ attacks the secondary carbocation formed at C-3, the final product (Compound A) will be:

```
CH₃
|
CH
|
CH₂
|
I
```

This corresponds to 2-iodopentane (C₅H₁₃I).

### Conclusion
The major product A formed from the reaction of 1-pentene with HI is **2-iodopentane**.

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