Nitrogen isotope effects, nucleophilic

Other workers have concluded that the transition state for the Menshutkin reaction is late with more nitrogen-alpha carbon bond formation than alpha carbon-leaving group bond rupture. For instance, Harris and coworkers51 found that the secondary alpha deuterium kinetic isotope effects (Table 8) decreased when a poorer nucleophile was used in the S v 2 reactions between 3,5-disubstituted pyridines and methyl iodide in 2-nitropropane at 25 °C (equation 38, Table 8). 

TABLE 7. The incoming nucleophile nitrogen kinetic isotope effects in Menshutkin reactions with various amines in several solvents ... 

The nucleophile in the S.v2 reactions between benzyldimethylphenylammonium nitrate and sodium para-substituted thiophenoxides in methanol at 20 °C (equation 42) can exist as a free thiophenoxide ion or as a solvent-separated ion-pair complex (equation 43)62,63. The secondary alpha deuterium and primary leaving group nitrogen kinetic isotope effects for these Sjv2 reactions were determined to learn how a substituent on the nucleophile affects the structure of the S.v2 transition state for the free ion and ion-pair reactions64. 

Oxygen-18, nitrogen-15 and -deuterium isotope effects in the transfer reactions of p-nitrophenyi acetate (PNPA) with various nucleophiles... 

The solvent deuterium isotope effect in the reaction of 359 with glyoxylate decreases from ( H2o/ D2o) °f 1-66 to ( H2o/ D2o) °f 1-12 with increasing pH from 1.25 to 6.43, respectively. 361 probably decarboxylates via a cyclic transition state. Transfer of the carboxylic proton takes place simultaneously with heavy-atom reorganization as indicated by small solvent DIE in the acid-catalysed reaction. The solvent DIE h2o/ D20 °f 1-20 at 1. M H+, observed in the reaction of 359 with pyruvic acid, is similar to the reaction of pyruvic acid with nitrosobenzene for which nucleophilic attack of nitroso nitrogen has been proposed395. 

Finally, reviews discussing nucleophile carbon knlku,61 nitrogen 14/A 15,68 and secondary a-deuterium69 kinetic isotope effects in SN2 reactions have been published. 

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