Final answer:
Markovnikov's rule explains the regioselectivity observed in the addition of halogens to unsymmetrical alkenes, where the hydrogen from a hydrogen halide attaches to the more substituted carbon, leading to the most stable carbocation intermediate and thus dictating the regiochemistry of the product.
Step-by-step explanation:
The student's question pertains to the observation made by chemist Vladimir Markovnikov on the regioselectivity of halogen addition to alkenes, which is often referred to as Markovnikov's rule in organic chemistry. When an unsymmetrical alkene reacts with a hydrogen halide, such as HCl or HBr, the hydrogen atom attaches to the carbon with the greater number of hydrogen atoms already bonded to it (the more substituted carbon), while the halide (chloride, bromide, etc.) attaches to the carbon with fewer hydrogen atoms (the less substituted carbon). This phenomenon is because the most stable carbocation intermediate is formed during the reaction, leading to the major product. This rule is a key concept when predicting regiochemistry of the addition of halogens to alkenes.