Question

Predict the major product(s) of the following reactions and explain their formation: -propene and HBr in presence of (Ph-C-O-O)2

Answer 1

The major product will be 1-BromoPropane.

Explanation:

When alkene reacts with H-X (halide) in the absence of peroxide it follows Markovnikov's Rule of electrophilic addition.

According to Markovnikov's Rule When a compound HX is added to an unsymmetrical alkene, the hydrogen becomes attached to the carbon with the most hydrogens attached to it already.

But in this reaction, benzoyl peroxide is there so will follow Anti Markovnikov's Rule. The peroxide effect is seen here. Here it occurs free radical chain reaction.

Mechanism of the reaction:

1. Chain initiation:
R-O-O-R -----> R-O* + *O-R
R-O* + H-Br -----> R-O-H + *Br
2. Chain propagation: 
When the bromine radical joins to the propene, it attaches so that a secondary radical is formed which is more stable than the primary radical which would be formed if it attached to the other carbon atom.

CH₃-CH=CH₂ + *Br -----> CH₃-*CH-CH₂Br

The redical again reacts with HBr to form 1- BromoPropane. (hydrogen addition step)

CH₃-*CH-CH₂Br + HBr -----> CH₃-CH₂-CH₂Br + *Br

Chain termination step:

thus two free radicals hit each other and produce a molecule of some sort. The process stops here because no new free radicals are formed.