14.1.5—The general unreactivity of alkanes

Alkanes have strong C–H and C–C sigma bonds and no strongly polar functional group. Polar reagents therefore have little incentive to react under ordinary conditions.

This is a kinetic and electronic explanation, not an absolute ban. Radical halogenation, combustion and cracking need suitable light, heat, oxygen or catalysts.

Bromine water is not rapidly decolourised by an alkane at room temperature, whereas an alkene reacts by electrophilic addition across C=C.

“Unreactive” does not mean chemically inert, and the explanation is not simply that alkanes are non-polar gases.