The principle organic compound formed in the reaction is
`CH_(2)= CH(CH_(2))_(3) COOH+ HBr overset("organic")overset("peroxide")(to) ` Major product

Options

A. `CH_(3) -underset(Br)underset(|)(CH)(CH_(2))_(3) COOH`
B. `underset(Br)underset(|)(CH_(2)) -CH_(2)- (CH_(2))_(3) COOH`
C. `CH_(2)=CH(CH_(2))_(3)COBr`
D. `CH_(2) =CHCH_(2) -CH_(2)-underset(Br)underset(|)(CH) - COOH`

Answer

To solve the problem, we need to determine the principal organic compound formed when the alkene `CH2=CH(CH2)3COOH` reacts with HBr in the presence of an organic peroxide. The key point to remember is that the reaction follows the anti-Markovnikov rule due to the presence of the peroxide.

### Step-by-Step Solution:

1. **Identify the Reactants**:
The reactants are:
- Alkene: `CH2=CH(CH2)3COOH`
- Hydrogen bromide (HBr)
- Organic peroxide (let's assume benzoyl peroxide as mentioned in the transcript)

2. **Understand the Reaction Mechanism**:
In the presence of organic peroxides, the addition of HBr to an alkene occurs via the anti-Markovnikov mechanism. This means that the bromine atom (Br) will attach to the carbon atom of the double bond that has more hydrogen atoms.

3. **Draw the Alkene Structure**:
The alkene can be represented as:
```
CH2
|
CH
|
CH2
|
CH2
|
COOH
```

4. **Apply the Anti-Markovnikov Rule**:
According to the anti-Markovnikov rule, the Br will attach to the carbon that has more hydrogen atoms. In this case, the double bond is between the first two carbon atoms (C1 and C2). C1 has two hydrogens, and C2 has one hydrogen. Therefore, Br will attach to C1.

5. **Form the Major Product**:
After the addition of HBr:
- The product will have Br attached to C1 and a hydrogen will be added to C2.
- The structure of the major product will be:
```
CH2Br
|
CH
|
CH2
|
CH2
|
COOH
```

6. **Write the Final Product**:
The major product formed from the reaction is:
```
CH2Br-CH(CH2)3COOH
```

### Final Answer:
The principal organic compound formed in the reaction is `CH2Br-CH(CH2)3COOH`.