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.
Source:
PAC, 1994, 66, 1077
(Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994))
on page 1174
Cite as:
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by
A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997).
XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic,
J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8.
https://doi.org/10.1351/goldbook.
