Which one of the following is a free-radical substituion reaction ?

Options

A.
B.
C.
D. `CH_(3)CHO + HCN to CH_(3)CH(OH)CN`

Answer

To determine which of the given reactions is a free-radical substitution reaction, we will analyze each option step by step.

### Step 1: Understand Free Radical Reactions
Free radical reactions typically involve the generation of free radicals, which are highly reactive species with unpaired electrons. These reactions often require specific conditions such as heat, light, or the presence of peroxides to initiate the formation of radicals.

**Hint:** Look for conditions that generate free radicals, such as heat or light.

### Step 2: Analyze the First Option
The first option involves boiling, which can generate free radicals. In this case, chlorine (Cl2) can react with an alkane (like methane) in the presence of heat or light, leading to the substitution of hydrogen atoms by chlorine atoms. This is a classic example of a free radical substitution reaction.

**Hint:** Boiling can lead to the generation of free radicals, especially with halogens.

### Step 3: Analyze the Second Option
The second option describes a reaction involving anhydrous aluminum chloride (AlCl3) and a hydrocarbon. This is a Friedel-Crafts alkylation reaction, which is an electrophilic substitution reaction. Here, AlCl3 acts as a Lewis acid to polarize the chlorine molecule, creating an electrophile that reacts with the aromatic compound. This does not involve free radicals.

**Hint:** Friedel-Crafts reactions are electrophilic and do not involve free radicals.

### Step 4: Analyze the Third Option
The third option involves a reaction where a nitro group (NO2) is added to a compound. This reaction is characterized by the attack of a nucleophile on an electrophile, making it a nucleophilic substitution reaction. Again, this does not involve free radicals.

**Hint:** Nucleophilic reactions involve electron-rich species attacking electron-poor species, not free radicals.

### Step 5: Analyze the Fourth Option
The fourth option involves a reaction with silver nitrate (AgNO2). This reaction is also a nucleophilic substitution, where a nucleophile attacks a positively charged center. This does not involve the generation of free radicals.

**Hint:** Look for reactions that involve nucleophiles and electrophiles, which indicate nucleophilic substitution.

### Conclusion
After analyzing all the options, we conclude that the first option, which involves boiling and the substitution of hydrogen by chlorine, is the only free radical substitution reaction.

**Final Answer:** The first option is a free-radical substitution reaction.