Anti - Markovinioff additio of HBr is not observed in

Options

A. propane
B. 1 - butene
C. but - 2- ene
D. pent - 2 - ene

Explanation

To solve the question regarding the Anti-Markovnikov addition of HBr, we need to analyze the conditions under which this reaction occurs and identify the compound where this addition is not observed.

### Step-by-Step Solution:

1. **Understanding Anti-Markovnikov Addition**:
- Anti-Markovnikov addition refers to the addition of HBr to alkenes where the hydrogen atom (H+) adds to the carbon with fewer hydrogen atoms, while the bromine (Br-) adds to the carbon with more hydrogen atoms. This occurs in the presence of peroxides.

2. **Identify the Type of Compounds**:
- The Anti-Markovnikov addition is typically observed in alkenes. We need to determine which of the given options is not an alkene or does not have the necessary structure for this addition.

3. **Evaluate Each Option**:
- **Option 1: Pentane** - Pentane is an alkane (C5H12) and does not have a double bond. Therefore, Anti-Markovnikov addition cannot occur here.
- **Option 2: 1-Butene** - 1-Butene (C4H8) has a double bond and an unequal number of hydrogens on the double-bonded carbons. Thus, Anti-Markovnikov addition can occur.
- **Option 3: 2-Butene** - 2-Butene (C4H8) has a double bond but has equal numbers of hydrogens on the double-bonded carbons, making Anti-Markovnikov addition not applicable.
- **Option 4: Pent-2-ene** - Pent-2-ene (C5H10) has a double bond and unequal hydrogen distribution on the double-bonded carbons, allowing for Anti-Markovnikov addition.

4. **Conclusion**:
- The compounds where Anti-Markovnikov addition of HBr is not observed are Pentane (Option 1) and 2-Butene (Option 3). However, since the question asks for a single answer, the best choice is **Option 1: Pentane**, as it is not an alkene at all.

### Final Answer:
**Anti-Markovnikov addition of HBr is not observed in: Option 1 - Pentane.**