Question

Ethylene reacts with $B{r}_2$ to give $1,2-\text{dibromoethane}$. The anti addition takes place due to the formation of which intermediate?

Answer 1

The anti addition takes place due to the formation of the cyclic bromonium ion intermediate
In the first stage of the reaction, one of the bromine atoms becomes attached to both carbon atoms with the positive charge being found on the bromine atom. A brominium ion is formed.


The bromonium ion is then attacked from the back by a bromide ion.