Why is #Br_2# an electrophile?

Question

Ava Andrews · Accepted Answer

Because the #Br-Br# bond is polarizable.

The halogen molecules have a large, polarizable electron cloud that (so we assume) can be distorted. #""^(delta+)X-X^(delta-)# representations are very common, and these explain the reaction of the halogens with electron rich olefin species. Interhalogen species, say #I-Br# can also undergo electrophilic substitution. The iodine end of the molecule is more polarizable. The bromine is more electronegative. With an unsymmetrical alkene, say propylene, that reacts with 1 equiv #I-Br#, which alkyl halides would you predict you would get?

Brooklyn Barber · Answer

undefined Br₂ is an electrophile because it contains a polar covalent bond, where the shared electrons are more attracted to one bromine atom than the other. This creates a partial positive charge on one bromine atom, making it electron-deficient and thus capable of accepting electrons from a nucleophile during a chemical reaction.

Ava Andrews · Answer

undefined Br2 is an electrophile because it can accept a pair of electrons from a nucleophile during a chemical reaction. In the case of Br2, each bromine atom has a strong affinity for electrons due to its high electronegativity. When Br2 reacts with a nucleophile, such as an alkene or an electron-rich species, one of the bromine atoms in the Br2 molecule becomes partially positively charged due to the polarization of the bond between the two bromine atoms. This partial positive charge makes the bromine atom electron-deficient, or "hungry" for electrons, and thus capable of acting as an electrophile by accepting a pair of electrons from the nucleophile to form a new covalent bond.