Armilenium

Armilenium is a C₁₁H₁₁ carbocation and was originally proposed as the first entirely organic sandwich compound. 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 in 1973. In subsequent ¹³C NMR experiments by Goldstein and Joseph P. Dinnocenzo in 1984, the C₁₁H₁₁ 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.

Sources

• Journal of the American Chemical Society, 1973, 95 (3), pp 935–936
• Advances in Physical Organic Chemistry, V. Gold, D. Bethell, pp. 366–367
• Annual Reports on the Progress of Chemistry, Royal Society of Chemistry (Great Britain), 1974, p. 221
• Accounts of Chemical Research, 1975, 8 (12), pp 413–420
• Journal of the American Chemical Society, 1981, 103, 6530-6532
• Journal of the American Chemical Society, 1984, 106, pp. 2473-2475