Term: umpolung
https://doi.org/10.1351/goldbook.U06551

Definition:
Any process by which the normal alternating donor and acceptor reactivity pattern of a chain, which is due to the presence of O or N heteroatoms, is interchanged. Reactivity umpolung is most often achieved by temporary exchange of heteroatoms (N, O) by others, such as P, S and Se. The original meaning of the term has been extended to the reversal of any commonly accepted reactivity pattern. For example, reaction of R–C≡CX (X = halide) as a synthon for 'R–C≡C+ (i.e. electrophilic acetylene) is an umpolung of the normal more common acetylide, R–C≡C− (i.e. nucleophilic) reactivity.

Related Terms:
1) electrophilic (http://doi.org/10.1351/goldbook.E02020).
2) nucleophilic (http://doi.org/10.1351/goldbook.N04249).

Source: PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1174 (https://doi.org/10.1351/pac199466051077)

Citation: 'umpolung' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.U06551

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