Norbornyl cation ESCA spectrum

Figure 6.16 Carbon b electron spectrum (ESCA) of (a) the 2-methylnorbornyl cation and (b) the norbornyl cation. From G. A. Olah, Angew. Chem. Int. Ed., 12, 173 (1973). Reproduced by permission of Verlag Chemie, GMBH.

Subsequently, Grunthaner reexamined the ESCA spectrum of the 2-norbornyl cation on a higher-resolution X-ray photoelectron spectrometer using highly efficient vacuum techniques.884 The spectrum closely matches the previously published spectra. Furthermore, the reported ESCA spectral results are consistent with the theoretical studies of Allen and co-workers885 on the classical and nonclassical norbomyl cation at the STO-3G and STO-4.31G levels. Using the parameters obtained by Allen and co-workers, Clark and co-workers were able to carry out a detailed... 

In a ESCA study with Mateescu and Riemenschneider38 we also succeeded to observe the ESCA spectrum of the norbornyl cation and compared it with that of the 2-methylnorbomyl cation and other trivalent carbenium ions, such as the cyclopentyl and methylcyclopentyl cations. The Is electron spectrum of the norbornyl... 

An essential argument against Fong s idea is provided by the data obtained by Olah from the ESCA spectrum of the 2-norbornyl cation. 

Further Kramer has measured the peak area ratio in the ESCA spectrum of the 2-norbomyl cation (from the figure published by Olah) and found it is not 2 5 (as required by the nonclassical ion model) but 4.5 1 or 6 1, depending on the method of measurement. Olah, however, points out that in the ESCA spectrum the main thing is not the ratio of peak areas which is often distorted due to admixtures coming from the vacuum systems and so can somewhat vary from experiment to experiment, but that of the AEb value. Finally, Kramer assumes the reported spectrum to belong to a neutral compound or a mixture of substances rather than to a stable ion. But according to Olah, the NMR spectra of the solutions under study before and after the recording of the ESCA spectrum are perfectly identical and coincide with that of the 2-norbornyl cation. 

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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