Free Radical Chlorination of Alkanes

Steps:

• Alkanes react with Cl₂ via free radical substitution, replacing one atom with chlorine.
• Initiation requires homolytic cleavage of Cl-Cl bond, typically by ultraviolet light to form Cl• radicals.
• Propagation involves H• abstraction from alkane by Cl•, followed by HCl formation and Cl• regeneration.
• Termination forms stable products like alkyl chloride, confirming hydrogen replacement.

Why C is correct:

• Free radical substitution replaces a hydrogen atom with chlorine; UV light initiates by generating chlorine radicals (Cl-Cl bond energy 242 kJ/mol, absorbed by UV).

Why the others are wrong:

• A: Carbon atoms are not replaced; thermal energy alone does not efficiently initiate chlorination.
• B: Hydrogen atom is replaced, but reaction requires UV light, not thermal energy.
• D: Carbon atoms are not replaced, despite UV light being required.

Final answer: C