The given reaction
`CH_3-CH_2-CH_3 overset(Br_2//hv)(rarr)CH_3-overset(Br)overset(|)(C )H-CH_3+HBr`
is an example of

Options

A. Nucleophilic substitution
B. Free radical substitution
C. Electrophilic substitution
D. Addition

Answer

To solve the question regarding the reaction of propane with bromine in the presence of light, we need to analyze the type of reaction taking place. Here’s a step-by-step breakdown:

### Step 1: Identify the Reactants and Conditions
The reaction involves propane (CH₃-CH₂-CH₃) and bromine (Br₂) under light (hv). The presence of light indicates that a photochemical reaction is occurring.

**Hint:** Look for the presence of light or heat in reactions; they often indicate radical mechanisms.

### Step 2: Understand the Mechanism
In the presence of light, Br₂ undergoes homolytic cleavage to form two bromine radicals (Br·). This is a key step in radical reactions.

**Hint:** Remember that light can break bonds, leading to the formation of radicals.

### Step 3: Radical Formation
The bromine radical can abstract a hydrogen atom from propane, leading to the formation of a propyl radical (CH₃-CH·-CH₃) and hydrogen bromide (HBr).

**Hint:** Identify which hydrogen is abstracted; consider the stability of the resulting radicals.

### Step 4: Stability of Radicals
The stability of the radicals formed is crucial. The propyl radical can be primary or secondary depending on which hydrogen is abstracted. The secondary radical is more stable due to hyperconjugation and inductive effects.

**Hint:** Recall the order of stability for radicals: tertiary > secondary > primary.

### Step 5: Formation of Products
The bromine radical can then react with the propyl radical to form the final product, which is bromopropane (CH₃-CH(Br)-CH₃) and regenerate HBr.

**Hint:** Look for the final products and ensure they match the expected outcomes from radical reactions.

### Step 6: Classify the Reaction
Since this reaction involves the formation of radicals and the substitution of hydrogen by bromine, it is classified as a free radical substitution reaction.

**Hint:** Free radical substitution typically involves the replacement of one atom or group in a molecule with another, facilitated by radicals.

### Conclusion
The given reaction is an example of **free radical substitution**.

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