The reaction between propene CH3-CH=CH2 and hydrogen bromide HBr to form 2-bromopropane CH3-CHBr-CH3 is an electrophilic addition reaction. The mechanism of this reaction involves two main steps:Step 1: Formation of carbocation intermediateThe alkene propene acts as a nucleophile, and the hydrogen bromide acts as an electrophile. The double bond of the propene attacks the hydrogen atom of HBr, breaking the H-Br bond. The electrons from the H-Br bond move to the bromine atom, forming a bromide ion Br- . This results in the formation of a carbocation intermediate, which is a positively charged carbon atom. In this case, it is a secondary carbocation CH3-CH+-CH3 .Step 2: Nucleophilic attack by bromide ionThe bromide ion Br- formed in the first step now acts as a nucleophile and attacks the positively charged carbon atom in the carbocation intermediate. This results in the formation of the final product, 2-bromopropane CH3-CHBr-CH3 .Overall, the mechanism of the reaction between propene and hydrogen bromide to form 2-bromopropane involves electrophilic addition, with the formation of a carbocation intermediate and a nucleophilic attack by the bromide ion.