Influence of the 7-Methoxy Group

From the above data on the dependence between an increase in the stabilizing effect of the substituent at C and a decrease in the barrier to the bridge-flipping it follows that at the limit the symmetrical nonclassical ion will be more stable 

1) the OCH3 group signal of the ion 450 is shifted to a high field in com[ ri n with that of the ion 451  

2) the character of the olefine proton splitting in the PMR qjectrum of the ion 450 is essentially different from that for ion 451  

3) if the ion 450 were unsymmetrical, then the double bond would affect but slightly the barrier for syn-anti-isomerization however, these barriers for ions 450 and 451 are rather different (14.7 and 11.7 kcal/mole)  

4) the energetic barriers of conversion of 7-substituted norbornadienyl ions into corresponding tropylium ions decrease consecutively in the series 7-H (23.5 kcal/ mole), 7-vinyl (17.1), 7-phenyl (15.9) at the same time for the 7-OCH3-substituted ion the barrier is very high (24.2). The conversion into a tropylium ion seems to favour the geometry of the unsymmetrical nonclassical ion. 

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