The halogen dance rearrangement is an
organic reaction in which a
halogen substituent moves to a new position on an
aromatic
In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satur ...
ring system. The reaction belongs to a class of organic reactions called
1,2-rearrangement A 1,2-rearrangement or 1,2-migration or 1,2-shift or Frank C. Whitmore, Whitmore 1,2-shift is an organic reaction where a substituent moves from one atom to another atom in a chemical compound. In a 1,2 shift the movement involves two adjacent atoms ...
s. The original halogen dance is the
base-catalysed rearrangement of 1,2,4-tribromobenzene to 1,3,5-tribromobenzene in liquid
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
with the
aniline
Aniline is an organic compound with the formula C6 H5 NH2. Consisting of a phenyl group attached to an amino group, aniline is the simplest aromatic amine. It is an industrially significant commodity chemical, as well as a versatile starti ...
/
potassium
Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosph ...
base system. The
intermediate in this reaction is an
aryl
In organic chemistry, an aryl is any functional group or substituent derived from an aromaticity, aromatic ring, usually an aromatic hydrocarbon, such as phenyl and naphthyl. "Aryl" is used for the sake of abbreviation or generalization, and "Ar ...
carbanion. The halogen dance concept can be extended from
benzene
Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms ...
derivatives to other aromatic systems as well, for instance
furan and
thiophene
Thiophene is a heterocyclic compound with the formula C4H4S. Consisting of a planar five-membered ring, it is aromatic as indicated by its extensive substitution reactions. It is a colorless liquid with a benzene-like odor. In most of its react ...
compounds.
The halogen dance rearrangement of iodooxazoles was studied by the Stambuli Group.
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References
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General references
*Participation of oligochlorobenzenes in the base-catalyzed halogen dance Martin H. Mach, Joseph F. Bunnett; J. Org. Chem.; 1980; 45(23); 4660-4666.
Rearrangement reactions