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Side Reactions in the Reaction of Methane and Bromine

You may remember that one of the chain termination steps produces ethane, CH3CH3.

{\bullet}CH_3 + {\bullet}CH_3 \longrightarrow CH_3CH_3

If bromine radicals hit that, you are going to get bromoethane and dibromoethane and so on – and in the course of those reactions you will get ethyl radicals which could themselves become involved in chain termination steps leading to propane (from methyl radical hitting ethyl radical) or butane (from two ethyl radicals combining), which could then start to undergo substitution – and on and on!

To be honest, all of these side products are going to be present in very small amounts because the reaction producing ethane won't, by chance, happen very often, but it nicely illustrates a typical organic chemistry problem – when you do a reaction in the lab to produce an organic chemical, a high proportion of your time is spent in purifying the product from all the side reactions that have gone on!