Basicity, nucleophilicity, and nucleofugality in the elimination–substitution reactions of β-phenylmercaptoethyl phenolates in DMSO–ethanol media

1994 ◽  
Vol 72 (2) ◽  
pp. 448-453 ◽  
Author(s):  
Hai-Qi Xie ◽  
Nguyen Truong ◽  
Erwin Buncel ◽  
J. Garfield Purdon
Keyword(s):  
Reaction Rate ◽  
Phenyl Group ◽  
Kinetic Studies ◽  
Substitution Reactions ◽  
Leaving Group ◽  
Partial Completion ◽  
Comparison Of The Results ◽  
Pure Dmso ◽  
Phenyl Vinyl

Kinetic studies have been performed on the base-promoted 1,2-elmination reactions of a series of β-phenylmercaptoethyl phenolates with potassium ethoxide in EtOH–DMSO media, yielding phenyl vinyl sulfide. The E2 mechanism was indicated by the absence of H/D exchange in the substrate when the reaction in EtOD–DMSO-d6 containing EtO− was carried to partial completion. The Brønsted coefficient values (βLG, effect of nucleofugality on reaction rate) of ca• 0.30 and ca• 0.98 were estimated for the reaction in pure DMSO and ethanol, respectively. Comparison of the results with reported reactions of substrates of similar structure revealed the important role of the phenyl group on sulfur, the leaving-group nucleofugality, and the medium basicity, in controlling the reaction pathways (elimination versus substitution).

SN2 Substitution Reactions at the Amide Nitrogen in the Anomeric Mutagens, N-Acyloxy-N-alkoxyamides

2009 ◽  
Vol 62 (7) ◽  
pp. 700 ◽  
Author(s):  
Katie L. Cavanagh ◽  
Stephen A. Glover ◽  
Helen L. Price ◽  
Rhiannon R. Schumacher
Keyword(s):  
Kinetic Studies ◽  
Model Reaction ◽  
Side Chain ◽  
Carboxylate Group ◽  
Amide Nitrogen ◽  
Substitution Reactions ◽  
Sn2 Reactions ◽  
Leaving Group ◽  
Rate Of Substitution

N-Acyloxy-N-alkoxyamides 1a are unusual anomeric amides that are pyramidal at the nitrogen because of bis oxyl substitution. Through this configuration, they lose most of their amide character and resemble α-haloketones in reactivity. They are susceptible to SN2 reactions at nitrogen, a process that is responsible for their mutagenic behaviour. Kinetic studies have been carried out with the nucleophile N-methylaniline that show that, like SN2 reactions at carbon centres, the rate constant for SN2 displacement of carboxylate is lowered by branching β to the nitrogen centre, or bulky groups on the alkoxyl side chain. Branching or bulky groups on the carboxylate leaving group, however, do not impact on the rate of substitution, which is mostly controlled by the pKA of the departing carboxylate group. These results are in line with computed properties for the model reaction of ammonia with N-acetoxy-N-methoxyacetamide but are in contrast to the role of steric effects on their mutagenicity.

Ligand Substitution Reactions

2007 ◽  
Author(s):  
Robert B. Jordan
Keyword(s):  
Transition State ◽  
Coordination Number ◽  
Reaction Rate ◽  
Ligand Substitution ◽  
Substitution Reactions ◽  
Definite Evidence ◽  
Oxidation Reduction ◽  
Leaving Group ◽  
Group 2 ◽  
Ligand Substitution Reactions

In ligand substitution reactions, one or more ligands around a metal ion are replaced by other ligands. In many ways, all inorganic reactions can be classified as either substitution or oxidation-reduction reactions, so that substitution reactions represent a major type of inorganic process. Some examples of substitution reactions follow: The operational approach was first expounded in 1965 in a monograph by Langford and Gray. It is an attempt to classify reaction mechanisms in relation to the type of information that kinetic studies of various types can provide. It delineates what can be said about the mechanism on the basis of the observations from certain types of experiments. The mechanism is classified by two properties, its stoichiometric character and its intimate character. The Stoichiometric mechanism can be determined from the kinetic behavior of one system. The classifications are as follows: 1. Dissociative (D): an intermediate of lower coordination number than the reactant can be identified. 2. Associative (A): an intermediate of larger coordination number than the reactant can be identified. 3. Interchange (I): no detectable intermediate can be found. The intimate mechanism can be determined from a series of experiments in which the nature of the reactants is changed in a systematic way. The classifications are as follows: 1. Dissociative activation (d): the reaction rate is more sensitive to changes in the leaving group. 2. Associative activation (a): the reaction rate is more sensitive to changes in the entering group. This terminology has largely replaced the SN1, SN2 and so on type of nomenclature that is still used in physical organic chemistry. These terminologies are compared and further explained as follows: Dissociative [D = SN1 (limiting)]: there is definite evidence of an intermediate of reduced coordination number. The bond between the metal and the leaving group has been completely broken in the transition state without any bond making to the entering group. Dissociative interchange (1d= SN1): there is no definite evidence of an intermediate. In the transition state, there is a large degree of bond breaking to the leaving group and a small amount of bond making to the entering group.

Empirical σ Molecular Orbital Parameters and their Correlation with Rates of Substitution Reactions in Quadrate Cr(III) and Co(III) Complexes

1971 ◽  
Vol 49 (9) ◽  
pp. 1497-1501 ◽  
Author(s):  
C. H. Langford
Keyword(s):  
Field Theories ◽  
Complete Analysis ◽  
Substitution Reactions ◽  
Spectral Parameters ◽  
Empirical Measures ◽  
Orbital Parameters ◽  
Spectral Bands ◽  
Leaving Group ◽  
The Relationship

Empirical measures of σ bonding involving metal 3d orbitals are derived from Perumareddi's (4) complete analysis of the quartet spectral bands of quadrate complexes in the families Cr(NH3)5Xn+ and Cr(OH2)5Xn+. These are shown to correlate with lability of X in the Cr(III) complexes and in Co(NH3)5Xn+ complexes in a sense indicating that relative reactivity is controlled by variation of ligand metal 3d σ interaction. The relationship between the two Cr(III) series implies that the non-labile ligands can labilize the leaving group in proportion to their σ donor capacities. This observation bears on some well-known difficulties in crystal field theories of reactivity. In evaluating the correlation of spectral parameters with reactivity, the role of solvation in reactivity of Cr(III) and Co(III) complexes is discussed with emphasis on the surprisingly small solvent effects that have been observed.

Role of Lys-226 in the Catalytic Mechanism ofBacillus StearothermophilusSerine HydroxymethyltransferaseCrystal Structure and Kinetic Studies†,‡

Biochemistry ◽  
2005 ◽  
Vol 44 (18) ◽  
pp. 6929-6937 ◽  
Author(s):  
Siddegowda Bhavani ◽  
V. Trivedi ◽  
V. R. Jala ◽  
H. S. Subramanya ◽  
Purnima Kaul ◽  
...  
Keyword(s):  
Catalytic Mechanism ◽  
Kinetic Studies

Probing the Role of Tyr 64 ofTreponema denticolaCystalysin by Site-Directed Mutagenesis and Kinetic Studies†

Biochemistry ◽  
2005 ◽  
Vol 44 (42) ◽  
pp. 13970-13980 ◽  
Author(s):  
Barbara Cellini ◽  
Mariarita Bertoldi ◽  
Riccardo Montioli ◽  
Carla Borri Voltattorni
Keyword(s):  
Kinetic Studies ◽  
Site Directed Mutagenesis ◽  
Directed Mutagenesis

Photocatalytic Degradation of Methyl Orange by TiO2/Schorl Photocatalyst: Kinetics and Thermodynamics

2015 ◽  
Vol 713-715 ◽  
pp. 2789-2792
Author(s):  
Huan Yan Xu ◽  
Xue Li ◽  
Yan Li ◽  
Ping Li ◽  
Wei Chao Liu
Keyword(s):  
Methyl Orange ◽  
Reaction Rate ◽  
Reaction Kinetic ◽  
Kinetic Studies ◽  
Reaction Rate Constant ◽  
Order Reaction ◽  
Solution Ph ◽  
Kinetics And Thermodynamics ◽  
Hoff Equation ◽  
Degradation Of Methyl Orange

An active dye, Methyl Orange (MO) was employed as the target pollutant to evaluate the photocatalytic activity of TiO2/schorl composite and the kinetics and thermodynamics of this process was emphasized in this work. Langmuir–Hinshelwood kinetic model was employed for the kinetic studies and the results revealed that the process of MO photocatalytic discoloration by TiO2/schorl composite followed one order reaction kinetic equation under different conditions. The reaction rate constant (k) increased with initial MO concentration decreasing. When the catalyst dosage or solution pH increased,kvalues increased and then decreased. The possible reasons for these phenomena were discussed. Finally, the thermodynamic parameters ΔG, ΔH, ΔSwere obtained by the classical Van't Hoff equation.

Alkene Difunctionalization Directed by Free Amines: Diamine Synthesis via Nickel-Catalyzed 1,2-Carboamination

2021 ◽  
Author(s):  
Taeho Kang ◽  
José Manuel González ◽  
Zi-Qi Li ◽  
Klement Foo ◽  
Peter Cheng ◽  
...  
Keyword(s):  
Nickel Catalyst ◽  
Room Temperature ◽  
Kinetic Studies ◽  
Fine Tuning ◽  
Secondary Amines ◽  
Protecting Group ◽  
Wide Range ◽  
Leaving Group ◽  
Primary And Secondary Amines ◽  
Reaction Proceeds

A versatile method to access differentially substituted 1,3- and 1,4-diamines via a nickel-catalyzed three-component 1,2-carboamination of alkenyl amines with aryl/alkenylboronic ester nucleophiles and N–O electrophiles is reported. The reaction proceeds efficiently with free primary and secondary amines without needing a directing auxiliary or protecting group, and is enabled by fine-tuning the leaving group on the N–O reagent. The transformation is highly regioselective and compatible with a wide range of coupling partners and alkenyl amine substrates, all performed at room temperature. A series of kinetic studies support a mechanism in which alkene coordination to the nickel catalyst is turnover-limiting.

scholarly journals Leaving Group Ability in Nucleophilic Aromatic Amination by Sodium Hydride–Lithium Iodide Composite

Synthesis ◽  
2019 ◽  
Vol 52 (03) ◽  
pp. 393-398
Author(s):  
Jia Hao Pang ◽  
Derek Yiren Ong ◽  
Kohei Watanabe ◽  
Ryo Takita ◽  
Shunsuke Chiba
Keyword(s):  
Nucleophilic Substitution ◽  
Methoxy Group ◽  
Sodium Hydride ◽  
Lithium Iodide ◽  
Substitution Reactions ◽  
Computational Approaches ◽  
Nucleophilic Substitution Reactions ◽  
Leaving Group ◽  
Leaving Group Ability

The methoxy group is generally considered as a poor leaving group for nucleophilic substitution reactions. This work verified the superior ability of the methoxy group in nucleophilic amination of arenes mediated by the sodium hydride and lithium iodide through experimental and computational approaches.

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