The 2-Norbornenyl Ion

Much interest has been shown for the solvolysis of esters of 2-exo-norbornenol and its homoallylic isomer — 3-nortricyclenol 337,339,340,349-352) 

Due to the negative inductive effect the introduction of a double bond decreases the acetolysis rates of both 2-exo- and 2-endo-norbomenyl brosylates as compared with saturated analogues (the numbers stand for the relative acetolysis rates of brosylates)  

The solvolysis rate of unsaturated exo-sulphonate is 7900 times as high as that of endo isomer, i.e. by far higher than that for saturated analogues ( 475). This is 

The major products of solvolysis of 2-exo- and 2-endo-norbomenyl or nortricyclyl halides or sulphonates are nortricyclyl derivatives 2-exo-norbomenyl derivatives are formed with a small yield. The predominant formation of nortricyclyl derivatives is associated with its higher stability compared to the norbomene one Even in the direct equilibrium between norbomene and nortricyclene the tricyclic isomer is predominant (3 1) at reflux temperature. This difference in the stability of products can be partially reflected on the activation energy for partitioning the cationic intermediates into bicyclic and tricyclic solvolysis products. 

Solvolysis of 2-exo-norbomenyl sulphonates tagged with on and C shows that the process is accompanied by skeleton rearrangements (30-50%). Judging by the extent of tag entanglement , part of the norbomenyl products (0-40%) is formed from the homoallylic ion 171, but the precursor of the main part is the symmetrical ion 173 in which the and atoms are equivalent. The tag entanglement, however, is less than if the symmetrical ion alone were formed. 

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For systems in which the homoallylic double bond is located unsymmetrically relative to the leaving group, like in 2-substituted norbomenes there is a comparatively small rate increase. At the same time in 7-anti-substituted norbomenes where a symmetrical position of the double bond contributes to intermediate formation of the 7-anti-norbornenyl (bishomocyclopropenyl) ion 19 the it-participation is strong Such an ion, according to quantum chemical calculations, is by 4 kcal/mole more stable than the 2-norbornenyl ion 171... 

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