Solvolysis of 2-Norbornyl Arenesulphonates

Acetolysis of the exo-brosylate 22 proceeds 350 times as fast as that of the endo-epimer 23 in the first case the configuration is completely retained but the rate of the complete racemization exceeds that of solvolysis. The solvolysis of endo isomer 

23 also results in the formation of exo acetate alone, but in this case 7-8% of optical activity is retained and no significant difference is observed between the rate of racemation and that of formation of 4-bromobenzenesulphonic acid. 

Reinvestigation of the reaction products by vapour-phase chromatography has confirmed the exclusive exo-configuration of the substitution products also, the reaction mixture was found to contain hydrocarbons. Thus, exo-brosylate 22 on ace-tolysis (at 25 °C) yields 95.6% of acetate and 4.4% of hydrocarbons endo-brosylate 23 at 75 °C forms a mixture of 87.3% of acetate and 12.7% of hydrocarbons. More than 99.7% of acetates have an exo configuration hydrocarbons are a mixture of nortricyclene and norbornene (39 1), 

The enhanced rate of solvolysis of the exo-isomer (350-fold) as compared to endo isomer is, according to Winstein, due to an intramolecular attack by cj-electrons of the C —C bond on in the transition state of the C —O bond heterolysis. In the endo epimer, since the stereoelectronic considerations require a backside attack, the participation of the C —C bond is impossible. The a-participation of the C —C bond is stereoelectronically feasible and would yield ion 24. This ion could only be attacked by a nucleophile from the endo-side but no such products have been isolated. Seemingly, the participation of the bond would bring about so high an 

If the forming ion of the 24 type is essentially stabilized by the substituent at C , then these unfavourable factors may be overcome. 

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