Addition of Br₂ to Alkyne

• The addition of Br₂ to an alkyne is analogous to adding Br₂ to an alkene.
• Once Br₂ approaches the nucleophilic alkyne, it becomes polarized.
• The π

• electrons, from the triple bond, can now attack the polarized bromine forming a C-Br bond and displacing the bromine ion.
• Now, you will get an intermediate electrophilic carbocation, which will immediately react with the bromine ion giving you the dibromo product.

First, you see the polarized Br₂ being attacked by the π electrons. Once you form the C-Br bond, the other bromine is released as a bromine ion. The intermediate here is a bromonium ion, which is electrophilic and reacts with the bromine ion giving you the dibromo product.