Cross-interaction constant , nucleophilic reactions

Gas-phase nucleophilic substitution reactions of Y-benzyl chlorides and X-phenoxide or X-thiophenoxide nucleophiles have been investigated by using the PM3 semiempirical MO method. The structure of the transition state was examined. The values of the gas-phase Hammett constants px and py are much greater than for the solution reactions, but a theoretical cross-interaction constant pxy (ca —0.60 for both phenoxides and thiophenoxides) agrees well with an experimental value of —0.62 for the thiophenoxide reactions in MeOH at 20 °C. Other work by the same group has involved theoretical studies of competitive gas-phase 5 n2 and E2 reactions of NCCH2CH2CI with HO and An ab initio method at the 6-31-l-G level was... 

A stepwise mechanism with a rate-limiting leaving group expulsion from the intermediate was proposed for the reactions of Z-aryl dimethyl- (43a), methylphenyl-(43b), and diphenyl-phosphinates (43c) with substituted anilines in DMSO at 333 K, based on the positive cross-interaction constants, The steric effects of the two ligands (R, R ) play a role in determining the reactivity of the phosphinates, but are relatively small compared to other phosphinate systems. A dominant frontside nucleophilic attack involving a hydrogen-bonded four-centre-type transition state (44) was proposed... 

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