monoadduct

Monoadduct is a term used in chemistry to denote a product formed when a single addition or covalent attachment occurs between two reacting partners, or when a substrate reacts with one equivalent of a reagent. The concept is used across organic, inorganic, and biochemical contexts. A monoadduct stands in contrast to diadducts or polyadducts, which result from a second or further addition at one or more reactive sites.

In organic chemistry, a substrate bearing an unsaturated bond or a reactive functional group can react with one equivalent of a reagent to yield a monoadduct. The outcome is governed by regioselectivity and stereochemistry depending on the mechanism of addition. For example, the addition of one equivalent of HCN to an aldehyde forms a cyanohydrin monoadduct, whereas excess reagent may produce further reaction at additional sites.

In biochemistry and pharmacology, monoadducts are common descriptors for the initial covalent attachment of a drug to a biomolecule. A classical example is the formation of a platinum-based drug monoadduct with a guanine base in DNA; subsequent reactions can generate diadduct crosslinks that disrupt replication and transcription.

Analytical methods such as NMR spectroscopy, mass spectrometry, infrared spectroscopy, and crystallography are used to characterize monoadducts, along with biochemical assays in relevant systems.

Overall, monoadducts denote a single, initial attachment event in a reaction sequence, and the term helps distinguish early-stage products from later crosslinked or multi-addition products.