According to Markownikoff's rule, which product is favored when an alkene reacts with HBr?

Markownikoff's rule states that when an unsymmetrical alkene reacts with a hydrogen halide, the hydrogen atom from the acid will attach to the carbon atom of the double bond that has the greater number of hydrogen atoms already. This preferential attachment leads to the formation of a more stable carbonium ion (or carbocation).

In this reaction, as the alkene adds HBr, the initially formed carbonium ion can exist as either primary, secondary, or tertiary. The stability of these carbonium ions varies significantly—tertiary carbonium ions are the most stable, followed by secondary and then primary. When HBr adds to the alkene, the most stable carbocation forms preferentially during the reaction pathway. Therefore, the product that is favored is the one that corresponds to a more stable carbonium ion because the stability of the intermediate is a driving force for the reaction's direction by lowering the activation energy and promoting the formation of the final product.

This understanding of the distribution of stability in the intermediary states helps to predict the major product of the reaction, which aligns with the concept presented in Markownikoff's rule.