Chemoselectivity

Chemoselectivity, in chemical reactions, denotes the propensity for a specific reaction pathway to occur among a set of potential alternatives.[1]

In an alternate definition, chemoselectivity pertains to the preferential reactivity of one functional group in the presence of others. This phenomenon is often influenced by the molecular connectivity alone, and may involve the use of protecting groups in more complex reactions. While predictions based on connectivity are generally deemed plausible, the physical outcome of a reaction depends on numerous factors that are typically challenging to predict with high precision (such as solvent effects, atomic orbital interactions, etc.).

Predicting chemoselectivity can be a complex task; however, it is not uncommon to observe selective outcomes in cases where numerous reactions are feasible. Examples include the greater relative chemoselectivity of sodium borohydride versus lithium aluminium hydride for the organic reduction of 4-nitro-2-chlorobenzonitrile to the corresponding aniline, 4-amino-2-chlorobenzonitrile. In another example, the compound 4-methoxyacetophenone is oxidized by bleach at the ketone group at high pH (forming the carboxylic acid) and oxidized by EAS (to the aryl chloride) at low pH.[2]