Norbornyl 1,2,4,7-tetramethyl

Of particular importance are recent results on the energetics of the exo-2,3-hydride shift in the 2,3-dimethyl-2-norbornyl and the l,2,3,4-tetramethyl-2-norbornyl cations. Line broadening studies reveal a free energy of activation of 6-6 and 7-3 kcal mole for this process in the respective ions (Huang eta/., 1973 Jones et a/., 1974). 

It would be very interesting for the problem of the existence of the nonclassical 2-norbornyl cation to determine the crystal structure of one of its salts. Due to the generally low stability of such salts, it was not possible to analyze a salt of the unsubstituted 2-norbornyl cation. Laube (1987) was, however, successful in obtaining a crystal structure of the l,2,4,7-aAZ//-tetramethyl-2-norbornyl cation (as salt with Sb2Fn, 7.102). 

Following the clarification of the structure of the norbornyl cation by spectroscopic methods, further study of the alkylnorbornyl cations has now been made. The detailed analyses of low-temperature n.m.r. results show that the 2-methyl-, 1,2-dimethyl-, and 1,2,3,3-tetramethyl-norbornyl cations are all classical species undergoing rapid Wagner-Meerwein rearrangement. A separate study of the hydrochlorination of (456) and subsequent methanolysis of the product (457) unequivocally demonstrates the importance... 

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