Intramolecular van der Waals-London Cohesions and Chemical Reactivity: The Transition State in the Bimolecular Nucleophilic Displacement Reaction of Halide Ion with Alkyl Halide

1960 ◽  
Vol 13 (2) ◽  
pp. 218 ◽  
Author(s):  
E Spinner
Keyword(s):  
Transition State ◽  
Halogen Atom ◽  
Significant Contribution ◽  
Chemical Reactivity ◽  
Alkyl Halide ◽  
Van Der Waals ◽  
Transition States ◽  
Displacement Reaction ◽  
Kcal Mole ◽  
Nucleophilic Displacement

The intramolecular London-van der Waals cohesions in the transition states Hal�-. . . CH3 . . . Hal�- in which both halogen atoms are identical should be greater than the following : Hal=F, 0.09 ; Hal=Cl, 0.64 ; Hal=Br, 0.94 ; Hal=I, 1.15 kcal/mole. It is concluded that these cohesions make a significant contribution to the observed increase in the velocity of the above displacement reaction as the polarizability of either entering or leaving halogen atom increases.

Topological aspects of chemical reactivity. On the possible use of similarity index in characterizing the transition state structure in concerted pericyclic reactions

1987 ◽  
Vol 52 (6) ◽  
pp. 1375-1385
Author(s):  
Robert Ponec
Keyword(s):  
Transition State ◽  
Chemical Reactivity ◽  
Transition States ◽  
Similarity Index ◽  
Pericyclic Reactions ◽  
State Structure ◽  
Transition State Structure ◽  
Topological Similarity

The use of the topological similarity index as a simple means for classification and characterization of the structure of the transition states in concerted pericyclic reactions is discussed. The suggested formulation makes it possible to bring a quantitative aspects into the empirical Dewar's classification of transition states in terms of aromaticity and/or antiaromaticity.

scholarly journals Effect of β,γ-CHF- and β,γ-CHCl-dGTP Halogen Atom Stereochemistry on the Transition State of DNA Polymerase β

Biochemistry ◽  
2012 ◽  
Vol 51 (43) ◽  
pp. 8491-8501 ◽  
Author(s):  
Keriann Oertell ◽  
Yue Wu ◽  
Valeria M. Zakharova ◽  
Boris A. Kashemirov ◽  
David D. Shock ◽  
...  
Keyword(s):  
Transition State ◽  
Dna Polymerase ◽  
Halogen Atom ◽  
Dna Polymerase Β

Roaming Reactions and Dynamics in the van der Waals Region

2020 ◽  
Vol 71 (1) ◽  
pp. 77-100 ◽  
Author(s):  
Arthur G. Suits
Keyword(s):  
Long Range ◽  
Internal State ◽  
Chemical Reactivity ◽  
Van Der Waals ◽  
Quantum Effects ◽  
Experimental Results ◽  
Unexpected Formation ◽  
Chemical Systems ◽  
Definition Of

Roaming reactions were first clearly identified in photodissociation of formaldehyde 15 years ago, and roaming dynamics are now recognized as a universal aspect of chemical reactivity. These reactions typically involve frustrated near-dissociation of a quasibound system to radical fragments, followed by reorientation at long range and intramolecular abstraction. The consequences can be unexpected formation of molecular products, depletion of the radical pool in chemical systems, and formation of products with unusual internal state distributions. In this review, I examine some current aspects of roaming reactions with an emphasis on experimental results, focusing on possible quantum effects in roaming and roaming dynamics in bimolecular systems. These considerations lead to a more inclusive definition of roaming reactions as those for which key dynamics take place at long range.

Ambident Heterocyclic Reactivity: Alkylation of 4-Substituted and 2,4-Disubstituted Benzimidazoles

1994 ◽  
Vol 47 (8) ◽  
pp. 1523 ◽  
Author(s):  
MR Haque ◽  
M Rasmussen
Keyword(s):  
Hydrogen Bonding ◽  
Transition State ◽  
Electrostatic Field ◽  
Transition States ◽  
Alkyl Halides ◽  
Methyl Group ◽  
Site Selectivity ◽  
Leaving Group ◽  
Standard Set ◽  
Specific Association

The N1/N3-alkylation patterns of 4-amino-, 4-methyl- and 4-nitro-benzimidazole anions, and their 2-methyl analogues, with a standard set of primary alkyl halides (in dimethylformamide, 30°) have been determined and compared. The observed regioselectivities are dominated by proximal effects-electrostatic field, non-bonded steric and in some cases specific association (hydrogen bonding)-the interplay of which is critically dependent on the (variable) geometries of the SN2 transition states involved, in particular on the N---C distance of the developing N-alkyl bonds. The presence of a symmetrically placed 2-methyl group produces an enhanced N1/N3 site selectivity, very sensitive to the loose-tight nature of the transition state. Halide leaving group effects on butylation regioselectivities of 2-unsubstituted, 2-ethoxy-, 2-methyl- and 2-chloro-4-methylbenzimidazole anions, whilst small, are consistent with a Bell-Evans-Polanyi analysis of SN2 transition state variations, with the earlier transition states of CH3(CH2)3I leading to reduced regioselectivities.

The log kexovs. log kendo correlation as a mechanistic criterion; on the mechanisms of solvolysis of norbornyl derivatives and base-catalyzed isotope exchange of norbornanones

1976 ◽  
Vol 54 (5) ◽  
pp. 678-684 ◽  
Author(s):  
Sujit Banerjee ◽  
Nick Henry Werstiuk
Keyword(s):  
Transition State ◽  
Exchange Rates ◽  
Isotope Exchange ◽  
Transition States ◽  
Substituent Effects ◽  
Proton Exchange ◽  
Hydrogen Deuterium Exchange ◽  
Rate Data ◽  
Hydrogen Deuterium ◽  
The Difference

Rate data for the acetolysis of exo-norbornyl-sulfonates have been correlated with those for the corresponding endo isomers. It is shown that the slopes of the log kexovs. log kendo plots reflect the difference in delocalization between the transition states derived from the exo and endo isomers, respectively. The log kexovs. log kendo plot, which is comprised of the parent norbornyl sufonate and its derivatives substituted at the 5, 6, and 7 positions, has a slope of 1.11 ± 0.08, which establishes that σ bridging is absent in the transition state obtained from the exo isomer. A similar analysis of base-catalyzed hydrogen–deuterium exchange rates of norbornanones reveals that exo proton exchange is more sensitive to substituent effects than the corresponding endo process.

Alkali metal ion catalysis in nucleophilic displacement by ethoxide ion on p-nitrophenyl phenylphosphonate: Evidence for multiple metal ion catalysis

2003 ◽  
Vol 81 (1) ◽  
pp. 53-63 ◽  
Author(s):  
Erwin Buncel ◽  
Ruby Nagelkerke ◽  
Gregory RJ Thatcher
Keyword(s):  
Alkali Metal ◽  
Transition State ◽  
Metal Ions ◽  
Metal Ion ◽  
Alkali Metal Ions ◽  
Phosphoryl Transfer ◽  
Alkali Metal Ion ◽  
Nucleophilic Displacement ◽  
Displacement Reactions ◽  
Metal Ion Catalysis

In continuation of our studies of alkali metal ion catalysis and inhibition at carbon, phosphorus, and sulfur centers, the role of alkali metal ions in nucleophilic displacement reactions of p-nitrophenyl phenylphosphonate (PNPP) has been examined. All alkali metal ions studied acted as catalysts. Alkali metal ions added as inert salts increased the rate while decreased rate resulted on M+ complexation with 18-crown-6 ether. Kinetic analysis indicated the interaction of possibly three potassium ions, four sodium ions, and five lithium ions in the transition state of the reactions of ethoxide with PNPP. Pre-association of the anionic substrate with two metals ions in the ground state gave the best fit to the experimental data of the sodium system. Thus, the study gives evidence of the role of several metal ions in nucleophilic displacement reactions of ethoxide with anionic PNPP, both in the ground state and in the transition state. Molecular modeling of the anionic transition state implies that the size of the monovalent cation and the steric requirement of the pentacoordinate transition state are the primary limitations on the number of cations that can be brought to bear to stabilize the transition state and catalyze nucleophilic substitution at phosphorus. The bearing of the present work on metal ion catalysis in enzyme systems is discussed, in particular enzymes that catalyze phosphoryl transfer, which often employ multiple metal ions. Our results, both kinetic and modeling, reveal the importance of electrostatic stabilization of the transition state for phosphoryl transfer that may be effected by multiple cations, either monovalent metal ions or amino acid residues. The more such cations can be brought into contact with the anionic transition state, the greater the catalysis observed.Key words: alkali metal ion catalysis, nucleophilic displacement at phosphorus, multiple metal ion catalysis, phosphoryl transfer.

ChemInform Abstract: “Transition-State Modeling” Does Not Always Model Transition States.

ChemInform ◽  
1989 ◽  
Vol 20 (27) ◽  
Author(s):  
M. J. SHERROD ◽  
F. M. MENGER
Keyword(s):  
Transition State ◽  
Transition States ◽  
Model Transition
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