Tricyclene, protonation

Sorensen and co-workers799-801 have studied the fate of observable camphene hydrocation 190 prepared from isoborneol 187, camphene 188, or tricyclene 189 in HSO3F acid medium (Scheme 5.74). The intermediate cycloalkenyl cation 191 can also be prepared by protonation of a-terpineol (192), sabine (193), and /3-pinene (194) (Scheme 5.75). 

Subsequently, the NMR, Raman, and ESCA spectra were measured for the norbornyl cation under stable ion conditions. The Raman spectrum exhibited similarities to the spectrum of tricyclene, and could be interpreted as indicating that the species under stable ion conditions is a protonated tricyclene. Such a corner-protonated tricyclene is simply an alternate description of the nonclassical ion. 

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