2- Methylnorbornyl cation

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.

Static classical ion [235] and the corresponding norbornyl- and cyclopentyl derivatives it was concluded that the charge delocalization through a-bridging is much less significant in [234] than in the partially bridged 2-methylnorbornyl cation. In this paper the classical structure [233] was also considered to be the major contributor to the observed nmr-shifts in the parent system. 

ESC A spectra-. Olah has shown that while in the spectrum of the 2-norbomyl cation the signal of the cation centre is separated from those of the other carbons by a barrier (AEb) of 1.5 eV, for the cyclopentyl cation it amounts to 4.3 eV this is due to far larger charge localization in classical carbocations. Kramer maintains that the cyclopentyl cation is an erroneous model to compare with the 2-norbomyl cation. However, in the spectrum of the 2-methylnorbornyl cation (which can obviously raise no objections as a model compound) the value of AE is 3.7 eV, i.e. again much higher than for the 2-norbomyl cation. 

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