Armilenium is a carbocation and was originally proposed as the first entirely organic

sandwich compound In organometallic chemistry, a sandwich compound is a chemical compound featuring a metal bound by haptic, covalent bonds to two arene (ring) ligands. The arenes have the formula , substituted derivatives (for example ) and heterocyclic deriv ...

. Named for its resemblance to an armillary sphere, NMR evidence for the carbocation was first described by Melvin J. Goldstein and Stanley A. Klein at

Cornell University Cornell University is a private statutory land-grant research university based in Ithaca, New York. It is a member of the Ivy League. Founded in 1865 by Ezra Cornell and Andrew Dickson White, Cornell was founded with the intention to tea ...

in 1973. In subsequent ¹³C NMR experiments by Goldstein and Joseph P. Dinnocenzo in 1984, the carbocation was generated under stable ion conditions at lower temperature and at higher magnetic field than previously possible. These experiments revealed the carbocation to be fluxional. Fitting of the dynamic NMR process ruled out the sandwich species even as an intermediate in the 20-fold degenerate rearrangement of the carbocation.

References

{{Reflist Carbocations