Kinetic Data and Nature of the 2-Norbomyl Ion

Compound Rela- tfve rate Compound Rela- tive rate Exo endo rate ratio Refe- rences 

It is more difficult to explain the deceleration of solvolysis for exo isomers. If the bulky substituent at C in the endo-position hinders the solvation of the arising classical 2-cation from the endo side, it is difficult to explain the hindrance to the solvolysis of compounds having hydrogens at the endo-position in C and C , e.g., 46, because for these compounds and for 22 there must be no difference in the ease of solvent approach from the endo-side. 

in the concept of classical ions the steric factors at C fail to account for the deceleration of solvolysis at C. At the same time the models show that for 6,6-dimethyl-2-exo-norbomyl brosylate 45 in the transition state leading to a non-classical ion the non-bonded interactions between the CHj groups on C and the hydrogens on C and are markedly increased. It is clearly seen from the scheme on the page 18. In the transition state of the nondassical ion formation unfavourable steric effects occur irrespective of whether the CH3 group at C is in the endo- or exo-position. Insteed, the substitution of the hydrogen by the CH3 group in C decreases the solvolysis rate of endo-tosylate (for steric reasons) but since the solvolysis rate of the exo epimer decreases too this confirms the participation of the C —C bond in the exo-tosylate ionization. 

Compounds Relative rate Compounds Relative rate Exo endo rate ratio 

---