Definition of umpolung

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 [triple bond] CX (X = halide) as a synthon for "R-CC+ (i.e. electrophilic acetylene) is an umpolung of the normal more common acetylide, R-CC- (i.e. nucleophilic) reactivity. SEEBACH (1979).

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element facts

General:

Name:	Symbol:
Group: Trans. Met.	Atomic weight:
Density @ 293 K: 10.07 g/cm3	Atomic volume:

States:

state (s, l, g):
melting point:	boiling point:
Heat of fusion:	Heat of vaporization:

Energies:

1st ionization energy:
electronegativity:	2nd ionization energy:
electron affinity:	3rd ionization energy:
Specific heat:?	heat atomization:

Oxidation & Electrons:

electron configuration:
minimum oxidation number:	maximum oxidation number:
min. common oxidation no.:	max. common oxidation no.:

Appearance & Characteristics:

structure:	color:
uses:	toxicity:
hardness:	characteristics:

Reactions:

reaction with air:	reaction with water:
reaction with 6M HCl:
reaction with 15M HNO3:	reaction with 6M NaOH:

Other Forms:

number of isotopes:	hydride(s):
oxide(s):	chloride(s):

Radius:

ionic radius (2- ion):	ionic radius (1- ion):
atomic radius:	ionic radius (1+ ion):
ionic radius (2+ ion):	ionic radius (3+ ion):

Conductivity:

thermal conductivity:
electrical conductivity:	polarizability:

Abundance:

source:
rel. abund. solar system:	abundance earth's crust:
cost, pure:	cost, bulk: