Selectivity

Selectivity is the degree to which a process, instrument, or system favors a particular outcome, substance, or input over others. It describes how selectively a method responds to a target relative to non-targets.

In chemistry, selectivity measures the preference of a reaction to form a specific product. Types include chemoselectivity (preference for a functional group), regioselectivity (position in a molecule), and stereoselectivity (stereochemistry). Quantities such as selectivity ratios or branching ratios express the bias.

Catalysis often seeks high selectivity, guiding reaction pathways toward the desired product and away from side products. Chemo-, regio-, and enantioselectivity arise from catalyst–substrate interactions, reaction conditions, and the reaction medium.

In pharmacology, drug selectivity refers to activity at a target relative to off-targets. A common measure is the selectivity index, comparing potency or affinity for the intended target against non-target receptors or enzymes.

In analytical and separation sciences, selectivity describes the ability to distinguish a target analyte from interferents. It depends on instrument design, chemical modifiers, and sample matrix; selectivity is reported as coefficients, limits of detection with respect to interferences, or validation tests.

Biology and ecology use selectivity to describe preferences in feeding, mate choice, or host use, and in biochemistry to denote binding specificity of receptors, antibodies, or enzymes.

Because selectivity affects efficiency, safety, and interpretability, it is a central consideration across chemistry, biology, medicine, and environmental sciences.