Limiting Unimolecular Nucleophilic Reactions—Effects of Structure and Solvent

2 LIMITING UNIMOLECULAR NUCLEOPHILIC REACTIONS. EFFECTS OF STRUCTURE AND SOLVENT 

31 Adapted with permission from S. Winstein and G. C. Robinson, J. Amer. Chem. Soc., 80, 175 (1958). Copyright by the American Chemical Society. 

32 In certain favorable cases of rearranging systems, the occurrence of internal return distinct from external ion-pair return can be demonstrated without recourse to optical rotation or isotopic labeling experiments. See S. Winstein and A. H. Fainberg, J. Amer. Chem. Soc., 80, 459 (1958) S. Winstein, P. E. Klinedinst, Jr., and E. Clippinger, J. Amer. Chem. Soc., 83, 4986 (1961). 

The simple S l mechanism, without ion pairs, predicts that the leaving group should not affect the products) we have seen in the previous section how the presence of ion pairs modifies this anticipated behavior. Since the leaving group is involved in the rate-determining step, it should have an important influence on rate. The experimental results confirm this prediction. 

An important neutral leaving group is N9, Diazotization of alkyl amines (Equation 5.11) leads to the unstable alkyl diazonium ions, which immediately lose nitrogen, leaving carbocations. 

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