Radicals, anti-Markovnikov halogen

The mechanism of the addition reaction under these conditions is not an ionic sequence rather, it is a much faster radical chain sequence. The reason is that the activation energies of the component steps of radical reactions are very small, as we observed earlier during the discussion of the radical halogenation of alkanes (Section 3-4). Consequently, in the presence of radicals, anti-Markovnikov hydrobromination simply outpaces the regular addition pathway. The initiation steps are... 

Synthesize the compound shown below from methylcyclopentane and 2-methylpropane using those compounds as the source of the carbon atoms and any other reagents necessary. Synthetic tools you might need include Markovnikov or anti-Markovnikov hydration, Markovnikov or anti-Markovnikov hydrobromination, radical halogenation, elimination, and nucleophilic substitution reactions. 

The reaction of an alkene with HBr and peroxide gives the bromide product with the bromine on the less substituted carbon in an anti-Markovnikov addition reaction. This reaction work wells with HBr, but not with HCl or HI because the bromine radical reacts in a selective manner. Differences in the reactivity of halogen radicals are addressed in Chapter 11, Section 11.9. 

Electrophilic addition of HCl or HBr to an alkene normally occurs with Mar-kovnikov regiochemistry, resulting in an alkyl halide with the halogen located at the more substituted carbon of the starting alkene. Since the presence of peroxides (ROOR) initiates a radical mechanism, HBr can also be added to an alkene with anti-Markovnikov orientation. Anti addition of bromine or chlorine to an alkene gives a trans-dibromo or dichloro product. 

Two reaction types that are commonly confused with one another are 8.478.5—addition of HBr to an alkene (Markovikov or anti-Markovnikov), and 15.2—radical halogenation using NBS or Br2 and light. This is especially confusing when substituting for an allylic H on an alkene. 

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