Alkane Reactivity Paradox?

📌 CONCEPT: The apparent paradox in alkane reactivity arises due to the distinction between thermodynamic stability and kinetic stability. Alkanes are thermodynamically stable, but under specific conditions, they can become kinetically unstable, facilitating reactions. This paradox is rooted in the difference between stability and reactivity.

📐 RULE / FORMULA: The key principle behind this phenomenon is the concept of bond-dissociation energy, where a lower bond-dissociation energy leads to higher reactivity. In the case of alkane chlorination, the formation of free radicals under high-energy conditions facilitates the reaction. The rule can be represented by the general equation: R-H + Cl2 → R-Cl + HCl.

💡 WORKED EXAMPLE: In the chlorination of methane, the reaction occurs through a free radical mechanism. Step 1: CH4 + Cl2 → CH3• + HCl + Cl•. Step 2: CH3• + Cl2 → CH3Cl• + Cl•. Step 3: CH3Cl• + HCl → CH3Cl + HCl, resulting in the formation of chloromethane.

⚠️ COMMON MISTAKE: Students often confuse thermodynamic and kinetic stability, assuming that an alkane's stability implies complete unreactivity. This misconception overlooks the complexities of chemical reactivity and the role of kinetic factors in facilitating reactions.