scholarly journals Influence of Long-Range Forces on the Transition States and Dynamics of NaCl Ion-Pair Dissociation in Water

2022 ◽  
Author(s):  
Dedi Wang ◽  
Renjie Zhao ◽  
John D. Weeks ◽  
Pratyush Tiwary
Keyword(s):  
Long Range ◽  
Transition States ◽  
Ion Pair

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

1989 ◽  
Vol 67 (1) ◽  
pp. 21-26 ◽  
Author(s):  
Zhu-Gen Lai ◽  
Kenneth Charles Westaway
Keyword(s):  
Nucleophilic Substitution ◽  
Isotope Effects ◽  
Transition States ◽  
Substituent Effects ◽  
Ion Pairing ◽  
Kinetic Isotope Effects ◽  
Ion Pair ◽  
Substitution Reactions ◽  
Kinetic Isotope ◽  
Free Ion

The secondary α-deuterium kinetic isotope effects and substituent effect found in the SN2 reactions between a series of para-substituted sodium thiophenoxides and benzyldimethylphenylammonium ion are significantly larger when the reacting nucleophile is a free ion than when it is a solvent-separated ion pair complex. Tighter transition states are found when a poorer nucleophile is used in both the free ion and ion pair reactions. Also, the transition states for all but one substituent are tighter for the reactions with the solvent-separated ion pair complex than with the free ion. Hammett ρ values found by changing the substituent on the nucleophile do not appear to be useful for determining the length of the sulphur–α-carbon bond in the ion pair and free ion transition states. Keywords: Isotope effects, ion pairing, nucleophilic substitution, SN2 reactions, transition states.

Rubidium pure long-range ion-pair molecules

2004 ◽  
Vol 66 (4) ◽  
pp. 485-491 ◽  
Author(s):  
T Ban ◽  
R Beuc ◽  
H Skenderović ◽  
G Pichler
Keyword(s):  
Long Range ◽  
Ion Pair

Long-Range Intramolecular S → N Acyl Migration: A Study of the Formation of Native Peptide Analogues via 13-, 15-, and 16-Membered Cyclic Transition States

2012 ◽  
Vol 77 (6) ◽  
pp. 2637-2648 ◽  
Author(s):  
Khanh Ha ◽  
Mamta Chahar ◽  
Jean-Christophe M. Monbaliu ◽  
Ekaterina Todadze ◽  
Finn K. Hansen ◽  
...  
Keyword(s):  
Long Range ◽  
Acyl Migration ◽  
Transition States ◽  
Cyclic Transition ◽  
Native Peptide ◽  
Peptide Analogues

Transition state geometry in the scission and formation of cyclopentane and cyclohexane oxiranes. Use of the dilatometer in studying mixed reactions of different orders

1979 ◽  
Vol 57 (18) ◽  
pp. 2444-2457 ◽  
Author(s):  
John W. Bovenkamp ◽  
Edward J. Langstaff ◽  
Robert Y. Moir ◽  
Robert A. B. Bannard
Keyword(s):  
Inductive Effect ◽  
Transition States ◽  
Accurate Method ◽  
High Specific Surface Area ◽  
Ion Pair ◽  
Third Order ◽  
Dipole Interactions ◽  
Conformational Effects ◽  
Cyclopentane Ring ◽  
Transition State Geometry

Two methods, one more accurate, the other more convenient, were developed by which the dilatometer could be used with concurrent reactions of the second and third order. The more accurate method, employing a dilatometer of high specific surface area and equipped with a stable and responsive thermometer, was used in studying as many as six simultaneous oxirane scissions in acid solution. Interlocking double comparisons were made between cyclohexane and cyclopentane ring systems, between systems possessing or lacking a methoxyl substituent and between others having the substituent in varying orientations, between charged and uncharged nucleophiles, and between transition states of different degrees of protonation. Searching experimental checks were therefore possible in four main areas: (i) a quantitative dissection of the inductive effect from steric and conformational effects, and from dipole–ion or dipole–dipole interactions with the nucleophile, (ii) a quantitative demonstration of three main differences between transition states based on 5- and 6-membered rings, (iii) a proof that syn-1,3-effects in the transition states are very charge dependent, being large and positive with unfavourably arranged dipoles, and small or perhaps negative with favourable arrangements, and (iv) a rejection of certain proposed ion-pair alternatives to the A2 mechanism.

scholarly journals Approach to form long-range ion-pair molecules in an ultracold Rb gas

2013 ◽  
Vol 87 (3) ◽  
Author(s):  
Adam Kirrander ◽  
Seth Rittenhouse ◽  
Marco Ascoli ◽  
Edward E. Eyler ◽  
Phillip L. Gould ◽  
...  
Keyword(s):  
Long Range ◽  
Ion Pair

scholarly journals Implementation of a k/k0 Method to Identify Long-Range Structure in Transition States during Conformational Folding/Unfolding of Proteins

Structure ◽  
2007 ◽  
Vol 15 (10) ◽  
pp. 1178-1189 ◽  
Author(s):  
Lovy Pradeep ◽  
Igor Kurinov ◽  
Steven E. Ealick ◽  
Harold A. Scheraga
Keyword(s):  
Long Range ◽  
Transition States ◽  
K0 Method

Pure long-range ion-pair Cs2 molecules

2001 ◽  
Vol 345 (5-6) ◽  
pp. 423-428 ◽  
Author(s):  
T Ban ◽  
H Skenderović ◽  
R Beuc ◽  
I Krajcar Bronić ◽  
S Rousseau ◽  
...  
Keyword(s):  
Long Range ◽  
Ion Pair

Isotope effects in nucleophilic substitution reactions XI. The effect of ion-pairing, substituents, and the solvent on SN2 transition states

1999 ◽  
Vol 77 (5-6) ◽  
pp. 879-889 ◽  
Author(s):  
Kenneth Charles Westaway ◽  
W Jiang
Keyword(s):  
Transition State ◽  
Nucleophilic Substitution ◽  
Substituent Effect ◽  
Isotope Effects ◽  
Transition States ◽  
Ion Pairing ◽  
Ion Pair ◽  
Leaving Group ◽  
Free Ion ◽  
Alpha Carbon

The secondary alpha deuterium and primary leaving group nitrogen KIEs and Hammett ρ values found for the free ion and ion-pair SN2 reactions between benzyldimethylphenylammonium ion and sodium para-substituted thiophenoxides in methanol at 20.000°C show how (i) ion-pairing of the nucleophile, (ii) a change in substituent in the nucleophile, and (iii) a change in solvent alters the structure of a Type II SN2 transition state. Ion-pairing shortens the weaker sulfur - alpha carbon (S—Cα) transition state bond significantly but does not alter the stronger alpha carbon - leaving group (Cα—N) transition state bond as the bond strength hypothesis predicts. However, the effect of ion pairing, i.e., the decrease in the S—Cα bond on ion-pairing, decreases as a more electron-withdrawing substituent is added to the nucleophile, and the S—Cα bond actually increases when the nucleophile is the p-chlorothiophenoxide ion. The identical Hammett ρ values of -0.85 and -0.84 for the free ion and ion-pair reactions, respectively, may be observed because, on average, the S—Cα bonds are identical in the free ion and ion-pair transition states. When a more electron-donating substituent is added to the nucleophile, an earlier transition state is found in both the ion-pair and free ion reactions. However, the substituent effect is smaller in the ion-pair reactions, presumably because the change in the negative charge on the sulfur atom with substituent is greater in the free ion than in the ion-pair. The substituent effect on transition state structure suggested by the KIEs is not predicted by any of the theories that are used to predict substituent effects on SN2 reactions. Both the secondary alpha deuterium and primary leaving group nitrogen KIEs and the Hammett ρ values indicate that the transition state is earlier when the solvent is changed from DMF to methanol as the "solvation rule for SN2 reactions" predicts. This probably occurs because an earlier, more ionic, transition state is more highly solvated (more stable) in methanol.Key words: nucleophilic substitution, SN2, isotope effect, transition state, substituent, ion-pair.

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