fluxional molecules

fluxional molecules,

molecules that exhibit rapid intramolecular rearrangements among their component atoms. As in structural isomerism and tautomerism (see isomerisomer
, in chemistry, one of two or more compounds having the same molecular formula but different structures (arrangements of atoms in the molecule). Isomerism is the occurrence of such compounds. Isomerism was first recognized by J. J. Berzelius in 1827.
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; tautomertautomer
, one of two or more structural isomers that exist in equilibrium and are readily converted from one isomeric form to another. Of the various types of tautomerism that are possible, two are commonly observed.
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), fluxional compounds maintain the same number of component atoms. At equilibrium, fluxional molecules may manifest many different isomers and fluctuate rapidly among them (for example, bullvalene, which has over 1,200,000 equivalent structures). The rearrangement process is usually detected by nuclear magnetic resonancemagnetic resonance,
in physics and chemistry, phenomenon produced by simultaneously applying a steady magnetic field and electromagnetic radiation (usually radio waves) to a sample of atoms and then adjusting the frequency of the radiation and the strength of the magnetic field
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 (NMR) spectroscopy, which can measure rearrangement rates occurring between 10−1 and 103 Hz.