摘要：

Rates of condensation of nine 1-substituted-2,4-dinitrobenzenes with piperidine in methanol to form 2,4-dinitrophenylpiperidine (II) have been measured. Three substituents, fluorine, nitro and p-toluenesulfonoxy, are displaced very rapidly while six substituents are displaced more slowly with remarkably little variation in rate amongst the six Since displacement of these six substituents involves the breaking of bonds between carbon and five other elements, this result indicates that bond-breaking has not made significant progress in the rate-determining transition states of these reactions The strictly SN2-like mechanism is thereby eliminated, but an alternate one-step mechanism is not. However, the facts are most agreeably interpreted in terms of the intermediate complex mechanism with the step in which the complex I is formed being rate determining. This result has the same significance for these nucleophilic substitutions that Melander's observation of the lack of a hydrogen isotope effect in nitration and bromination had for those reactions. Interesting complications were encountered in several of the reactions studied, but these did not prevent satisfactory determination of the desired rate coefficients.

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