Alkanes

Alkanes and free radicals

Alkanes are saturated hydrocarbons, fairly unreactive because C–C and C–H bonds are strong and non-polar. They're used as fuels: complete combustion gives CO₂ and H₂O; incomplete gives CO and soot. Cracking breaks long chains into shorter alkanes and alkenes (thermal: high T and p; catalytic: zeolite, lower T). With Cl₂ or Br₂ in UV light, alkanes undergo free-radical substitution: initiation ($\mathrm{Cl_2\rightarrow2Cl^\bullet}$), propagation ($\mathrm{Cl^\bullet+CH_4\rightarrow HCl+{}^\bullet CH_3}$; $\mathrm{{}^\bullet CH_3+Cl_2\rightarrow CH_3Cl+Cl^\bullet}$), termination (two radicals join). The mixture of products is a disadvantage. Cl• radicals from CFCs destroy ozone catalytically.