What is the most likely product to form when 4-methyl-1-pentene reacts with excess Br2? Please show the structural formula. What type of reaction is this?

1 Answer
Jun 21, 2018


The most likely product is 1,2-dibromo-4-methylpentane.


The reaction of an alkene with bromine gives a vicinal dibromide (a 1,2-dibromide).

Thus, the reaction of bromine with 4-methylpent-1-ene gives 1,2-dibromo-4-methylpentane.


The mechanism

The electrons in the π bond of the approaching alkene induce a dipole in the highly polarizable #"Br-Br"# bond.

The π electrons attack the partially positive #"Br"# atom, displacing a bromide ion.

The #"Br"# atom then joins to the other alkene carbon and forms a cyclic bromonium ion.

Step 1

In a second step, the #"Br"^"-"# attacks the more substituted carbon of the bromonium ion, forming a 1,2-dibromoalkane.

Step 2

This reaction is an example of electrophilic addition to an alkene.