Neighboring group participation, studies

Evidence comes from comparative rate studies.216 Thus 71 was hydrolyzed about 105 times faster than benzamide (PhCONH2) at about the same concentration of hydrogen ions. That this enhancement of rate was not caused by the resonance or field effects of COOH (an electron-withdrawing group) was shown by the fact both o-nitrobenzamide and terephthal-amic acid (the para isomer of 71) were hydrolyzed more slowly than benzamide. Many other examples of neighboring-group participation at a carbonyl carbon have been reported.2 7 It is likely that nucleophilic catalysis is involved in enzyme catalysis of ester hydrolysis. 

The conclusions reached by Isbell8 and other workers3-4 5 thus rendered clear the possible influence of neighboring-group participation on the stereochemical path of reaction. But the really profound effect that neighboring-group participation may have on the rate of reaction was not recognized in carbohydrate chemistry until after the discovery of this phenomenon by Winstein and coworkers. For example, a study by these... 

Gierer J, Petterson I (1977) Study on the condensation of lignins in alkaline media (2) Formation of stilbene and arylcoumaran structures through neighboring group participation reactions Can J Chem 55 593-599... 

The effect of a heteroatom 0 to the oxirane ring has been studied in the reaction of monosubstituted oxiranes 131 and benzylamine. If X = 0, the reaction occurs via the transition state 132 with neighbouring-group participation. Neighboring-group participation has similarly been observed in the reactions of mono- and tri-substituted oxiranes and )3-substituted primary amines. The product ratio of the aminoalcohols formed from the reactions of a-vinyloxiranes and primary amines depends on the geometry of the oxirane.Base-catalyzed addition of oxiranes to oximes leads not only to 0-alkyl but to A -alkyl derivatives (Eq, 319). ... 

---