Regioselectivity is preferential reaction at one of several constitutionally distinct sites or orientations. It concerns which bonds form where, rather than the configuration of the resulting stereocenters.
For example, adding a reagent across an unsymmetrical alkene can place its two components in either orientation, producing different constitutional isomers. Electronic effects, steric interactions, and the catalyst determine the product ratio. A reaction can be strongly regioselective but weakly enantioselective, since site preference and handedness are independent questions.
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Regioselectivity refers to the preference of a chemical reaction to occur at one specific location over another in a molecule that contains multiple reactive sites. This selectivity is particularly significant in organic chemistry, where a molecule may have several functional groups or double bonds that can potentially react. For example, in the case of electrophilic addition reactions or substitutions, a reagent might attack different positions on a substrate. Regioselectivity indicates which position the reagent preferentially reacts with, leading to a major product.