# Why is HBr an electrophile?

Jan 26, 2017

Because bromine is electronegative with respect to hydrogen....

#### Explanation:

Because of the difference in electronegativity, we could represent the hydrogen bromide molecule as ""^(+delta)H-Br^(delta-); the hydrogen is conceived to have a partial positive charge and tends to react with electron-rich species such as $\text{olefins}$, or $\text{hydroxide ions}$.

With $\text{olefins}$:

$R C H = C {H}_{2} + H - B r \rightarrow B {r}^{-} + R {H}^{+} C - C {H}_{3}$

(the alternative substitution is thermodynamically disfavoured, cf. Markownikow's rule.)

And then,

$R {H}^{+} C - C {H}_{3} + B {r}^{-} \rightarrow R \left(H\right) \left(B r\right) C - C {H}_{2} B r$