ChemInform Abstract: Isotope Effects in Nucleophilic Substitution Reactions. Part 6. The Effect of Ion Pairing on the Transition State Structure of SN2 Reactions

ChemInform ◽  
1988 ◽  
Vol 19 (46) ◽  
Author(s):  
K. C. WESTAWAY ◽  
Z. LAI
Keyword(s):  
Transition State ◽  
Nucleophilic Substitution ◽  
Isotope Effects ◽  
Ion Pairing ◽  
State Structure ◽  
Transition State Structure ◽  
Substitution Reactions ◽  
Nucleophilic Substitution Reactions ◽  
Sn2 Reactions

Isotope effects in nucleophilic substitution reactions. VI. The effect of ion pairing on the transition state structure of SN2 reactions

1988 ◽  
Vol 66 (5) ◽  
pp. 1263-1271 ◽  
Author(s):  
Kenneth Charles Westaway ◽  
Zhu-Gen Lai
Keyword(s):  
Transition State ◽  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Isotope Effects ◽  
Ion Pair ◽  
State Structure ◽  
Transition State Structure ◽  
Substitution Reactions ◽  
Sn2 Reactions ◽  
Kinetic Isotope

Spectroscopic and conductivity studies of sodium thiophenoxide solutions in four different solvents and the secondary α-deuterium kinetic isotope effects found in the presence of 15-crown-5 ether demonstrate that the secondary α-deuterium kinetic isotope effect and transition state structure for the SN2 reaction between sodium thiophenoxide and n-butyl chloride are significantly different, depending on whether the ionic reactant is a solvent-separated ion-pair complex or a free ion. In all three solvents in which the form of the ionic reactant changes, a smaller isotope effect and tighter transition state are found for the reaction with the ion-pair complex.

Isotope effects in nucleophilic substitution reactions X. The effect of changing the nucleophilic atom on ion-pairing in an SN2 reaction

1998 ◽  
Vol 76 (6) ◽  
pp. 758-764 ◽  
Author(s):  
Yao-ren Fang ◽  
Zhu-gen Lai ◽  
Kenneth Charles Westaway
Keyword(s):  
Transition State ◽  
Nucleophilic Substitution ◽  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Isotope Effects ◽  
Substituent Effects ◽  
Ion Pairing ◽  
State Structure ◽  
Transition State Structure ◽  
Kinetic Isotope

The effect of ion-pairing in an SN2 reaction is very different when the nucleophilic atom is changed from sulfur to oxygen, i.e., changing the nucleophile from thiophenoxide ion to phenoxide ion. When the nucleophile is sodium thiophenoxide, ion-pairing markedly alters the secondary α -deuterium kinetic isotope effect (transition state structure) and the substituent effect found by changing the para substituent on the nucleophile. When the nucleophile is sodium phenoxide, ion-pairing does not significantly affect the secondary α -deuterium or the chlorine leaving group kinetic isotope effects (transition state structure) or the substituent effects found by changing a para substituent on the nucleophile or the substrate. The different effects of ion-pairing may occur because the electron density on the hard oxygen atom of the sodium phenoxide is not affected significantly by ion-pairing.Key words: nucleophilic substitution, SN2, kinetic isotope effect, transition state, substituent effects, ion-pair.

ρ as a quantitative measure of transition state structure

1979 ◽  
Vol 57 (3) ◽  
pp. 255-257 ◽  
Author(s):  
Bo-Long Poh
Keyword(s):  
Free Radicals ◽  
Hydrogen Atom ◽  
Transition State ◽  
Nucleophilic Substitution ◽  
Electrophilic Substitution ◽  
Quantitative Measure ◽  
Hydrogen Atom Abstraction ◽  
State Structure ◽  
Transition State Structure ◽  
Substitution Reactions

The values of the Brønsted exponent for several examples of nucleophilic substitution reactions, aromatic electrophilic substitution reactions, and hydrogen atom abstraction from toluene by free radicals have been calculated from the ρ values of the corresponding reactions. The magnitude of the Brønsted exponent is shown to indicate the degree of charge developed in the transition state structure.

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