Fluxional molecule

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Fluxional molecules are molecules which can undergo a "self" reaction wherein bonds rearrange to a structurally identical molecule. Isotopic labelling, however, can demonstrate that bonds have actually shifted. In organic chemistry, this does not include torsional changes (such as amine flipping, cyclohexane flips, or syn-gauche rotations around di-methylene groups). The archetypal example is the cope rearrangement of hexadiene. More spectacular is bullvalene. Other mechanisms of fluxional molecules include "ring-whizzing" in cyclopentadiene.

In inorganic chemistry, fluxional molecules include geometric rearrangements, such as that undergone by iron carbonyl.