Markovnikov’s rule

Markovnikov’s rule is a fundamental principle in organic chemistry that describes the predictable outcome of addition reactions involving alkenes and protic acids. It’s a powerful tool for predicting the regioselectivity – specifically, which carbon atom within the double bond will become attached to the added hydrogen and halide. The rule states that when a protic acid (such as hydrogen halide, like HCl or HBr) reacts with an unsymmetrical alkene, the hydrogen atom of the acid will preferentially add to the carbon of the double bond that already carries more hydrogen substituents. Conversely, the halide ion (Cl⁻, Br⁻, etc.) will add to the carbon atom with fewer attached hydrogen atoms. This preferential addition occurs because the formation of the more stable carbocation intermediate drives the reaction. Understanding Markovnikov’s rule is crucial for controlling and anticipating the products of many important organic transformations.