# Hydrohalogenation

## Key Questions

• If more than one reaction could occur between a set of reactants under the same conditions giving products that are constitutional isomers and if one product forms in greater amounts than the others, the overall reaction is said to be regioselective.

Typically this is the addition of $H X$ $\left(X = C l , B r , I\right)$ to an olefin, $R - C H = C {H}_{2}$...

#### Explanation:

And the reaction follows the general scheme...

$R - C H - C {H}_{2} + H X \rightarrow {\underbrace{R \stackrel{+}{C} H C {H}_{3}}}_{\text{secondary carbocation}} + {X}^{-}$

$R \stackrel{+}{C} H C {H}_{3} + {X}^{-} \rightarrow R C H \left(X\right) C {H}_{3}$

This reaction follows so-called $\text{Markownikow selectivity}$,,the more substituted alkyl halide is favoured. Anyway, you are going to have to read your text...