Camphene hydrochloride solvolysis

The relative rates of solvolysis of camphene hydrochloride and t-butyl chloride indicate that the free energy of activation is 5 kcal mole higher with the latter compound. This might be attributed either to non-classical stabilization of the camphenyl transition state... 

We have accounted for the observed change in carbon skeleton, but we have not answered two questions that have plagued the organic chemist for a generation. Why is only the exo chloride, isobornyl chloride, obtained, and none of its endo isomer, bornyl chloride Why does camphene hydrochloride undergo solvolysis thousands of times as fast as, say, fert-butyl chloride To sec the kind of answers that have been given, let us turn to a simpler but basically similar system. 

ProUem 28.19 (a) Show how a nonclassical ion intermediate could account for both the stereospecificity and the unusually fast rate (if it is unusually fast) of rearrangement of camphene hydrochloride into isobomyl chloride, (b) How do you account for the fact that optically active product is formed here, in contrast to what is obtained from solvolysis of norbomyl compounds ... 

The results (4) do not support the conclusion that the rates for the norbomyl derivatives exhibit major enhancements. For example, the rate of solvolysis of camphene hydrochloride (/) is faster than that of the tetraniethylcyclopentyl chloride (7) by a factor of only 5.7. Such a factor is far too small to argue for a major new stabilizing phenomenon in the ion from 1. Removal of the gem-dimethyl substituents decreases the rate from 13,600 for 1 to 355 for 8. A similar effect is observed in the cyclopentyl derivatives, 7 and 9. These changes in reactivity are far more compatible with relief of steric strain13 than with resonance stabilization of the cations 12 ... 

There is evidence that a bonds can also participate in the formation of nonclassical carbocation intermediates in solvolysis reactions. In the Wag-ner-Meerwein rearrangement, camphene hydrochloride (45) rearranges to isobornyl chloride (46). It is possible to write a mechanism in which... 

An important difference between the theories behind Figs. 1 and 2 is that one expects from the former that the solvolysis of camphene hydrochloride (12) would be accelerated because it should lead to a synartetic ion (enter and leave from the right-hand side of Fig. 1), whereas it would not be accelerated if the latter theory is correct. Ethanolysis of camphene hydrochloride (12) occurs about 6000 times faster than that of r-butyl chloride but only 2.5 times faster than that of 1,2,2,5,5-pentamethyl cyclopentyl chloride (13). Hence the decision as to whether the ethanolysis of (4) is accelerated depends on which model reaction is chosen for the nonassisted... 

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