Question

1) explain how a nonpolar molecule like bromine can act as an electrophile?

2) why does performing some of the SE2 reactions at 0 degrees Celsius allow you to identify the order of reactivity more definitively?

Answer 1

1)

Bromine as an electrophile Since two identical bromine atoms are joined together in the bromine molecule there is no reason why one atom should pull the bonding pair of electrons
In fact, bromine is a very polarisable molecule - in other words, the electrons in the bond are very easily pushed to one end or the other. As the bromine molecule approaches the ethene, the electrons in the pi bond tend to repel the electrons in the bromine-bromine bond, leaving the nearer bromine slightly positive and the further one slightly negative. The bromine molecule therefore acquires an induced dipole which is automatically lined up the right way round for a successful attack on the ethene.

Source

http://www.chemguide.co.uk/mechanisms/eladd/symbr2tt.html

2)