n-Pentane `underset(hv)overset(Cl_(2))rarr(A)` (no. of total product)

Options

A. 2
B. 3
C. 4
D. 5

Answer

To determine the total number of products formed when n-pentane reacts with chlorine (Cl₂) under ultraviolet (UV) light, we need to analyze the reaction mechanism and the possible products formed through free radical substitution.

### Step-by-Step Solution:

1. **Identify the Structure of n-Pentane**:
- n-Pentane has the molecular formula C₅H₁₂ and its structure is:
```
CH₃-CH₂-CH₂-CH₂-CH₃
```

2. **Understand the Reaction Mechanism**:
- The reaction of n-pentane with Cl₂ in the presence of UV light proceeds via a free radical mechanism, which consists of three main steps: initiation, propagation, and termination.

3. **Initiation Step**:
- The Cl₂ molecule dissociates into two chlorine radicals (Cl•) under UV light:
```
Cl₂ → 2 Cl•
```

4. **Propagation Steps**:
- The chlorine radicals can abstract hydrogen atoms from n-pentane, leading to the formation of different alkyl radicals and products. The possible sites for hydrogen abstraction in n-pentane are:
- Primary hydrogens (from CH₃ groups)
- Secondary hydrogens (from CH₂ groups)
- The reaction can lead to different products based on which hydrogen is replaced by chlorine.

5. **Identify Possible Products**:
- **Substitution at Primary Carbons**:
- If Cl replaces a primary hydrogen (from CH₃), the product is 1-chloropentane (CH₃-CH₂-CH₂-CH₂-CH₂Cl).
- **Substitution at Secondary Carbons**:
- If Cl replaces a secondary hydrogen (from CH₂), the product is 2-chloropentane (CH₃-CHCl-CH₂-CH₂-CH₃). This product can exist as two optical isomers (R and S) due to the presence of a chiral center.

6. **Count the Unique Products**:
- From the analysis:
- 1-chloropentane (1 product)
- 2-chloropentane (2 products due to chirality)
- 3-chloropentane (1 product, as it does not create a chiral center)
- Therefore, the total number of unique products is:
- 1 (from primary) + 2 (from secondary) + 1 (from tertiary) = 4 products.

### Final Answer:
The total number of products formed when n-pentane reacts with Cl₂ under UV light is **4**.