Abstract
The azide competition factors ( k N 3 ,−/ k SOH) of cyclopentyl mesylate ( 1), 1-methylcyclopentyl chloride ( 2), cyclohexyl brosylate ( 3), benzhydryl chloride ( 4), benzhydryl bromide ( 5), 3β-cholestanyl brosylate ( 6), 3α-cholestanyl brosylate ( 7), 2-methyl-2-adamantyl chloride ( 8), 1-adamantyl bromide ( 9) and 2-adamantyl tosylate ( 10) were determined. Tertiary substrates ( 2, 8, 9) invariably gave lower k N 3 −/ k SOH values than secondary ones ( 1, 3, 4, 5, 7); opposite from what is expected on the basis of the stabilities of the respective free carbanium ions. This was explained by the attack of the nucleophile on ion pair(s) rather than on free carbonium ions. The magnitude of the competition factor seems to yield useful mechanistic information only in two extreme cases, i.e. direct displacement (S N2) and free stable carbonium ions (tertiary aromatic substrates-dissociative S N1 mechanism). In all other cases, especially with secondary substrates, the mechanistic evaluation of the k N 3 −/ k SOH values is ambiguous and in our opinion of doubtful value.
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