The reaction mechanism for the addition of HBr to propene according to quantum chemical calculations involves a two-step process:1. Formation of a carbocation intermediate:In the first step, the pi bond of the propene C=C reacts with the hydrogen atom of the HBr molecule. The hydrogen atom forms a bond with the less substituted carbon atom of the double bond Markovnikov's rule , resulting in the formation of a carbocation intermediate. The bromide ion Br- is generated as a leaving group.2. Nucleophilic attack by the bromide ion:In the second step, the bromide ion Br- acts as a nucleophile and attacks the carbocation intermediate, forming a bond with the positively charged carbon atom. This results in the formation of 2-bromopropane as the final product.Quantum chemical calculations provide insights into the electronic structure, energetics, and transition states involved in this reaction mechanism. These calculations help to understand the factors that influence the reaction rate and selectivity, such as the stability of the carbocation intermediate and the activation energy barriers for each step.