Question

Why is `HBr` an electrophile?

Answer 1

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 `"olefins"`, or `"hydroxide ions"`.

With `"olefins"`:

`RCH=CH_2 + H-Br rarr Br^(-) + RH^(+)C-CH_3`

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

And then,

`RH^(+)C-CH_3+Br^(-) rarrR(H)(Br)C-CH_2Br`