ELECTRONIC EFFECTS IN E2 REACTIONS: II. t-BUTOXIDE-INDUCED ELIMINATIONS OF 2-METHYL-3-PENTYL ARENESULFONATES

1965 ◽  
Vol 43 (5) ◽  
pp. 1282-1292 ◽  
Author(s):  
Allan K. Colter ◽  
Donald R. McKelvey
Keyword(s):  
Transition State ◽  
Dimethyl Sulfoxide ◽  
Vapor Phase ◽  
Rate Constants ◽  
Equilibrium Mixture ◽  
Second Order ◽  
Electronic Effects ◽  
Electronic Nature ◽  
Leaving Group ◽  
Electron Withdrawal

As part of a study of the influence of electronic effects imposed by the leaving group on orientation in E2 reactions, a study of elimination in a series of 2-methyl-3-pentyl arenesulfonates (I) has been carried out. The compositions of the olefin mixtures resulting from reaction of selected members of this series with potassium t-butoxide in t-butanol (1a, Id), 50% (by volume) t-butanol – dioxane (Ia–Ig), 25% (by volume) t-butanol – dioxane (Id–If), and 25% (by volume) t-butanol – dimethyl sulfoxide (Ia, Id, If, Ig), at 50 °C, have been determined using vapor phase chromatography. Second-order rate constants were measured for these reactions in t-butanol (Ie), and 50% t-butanol – dioxane (Ia, Ic–Ig) at 50 °C and in 25% t-butanol – dimethyl sulfoxide (Ia, Id, Ie) at 25 °C.The compositions of the olefin mixtures vary in a fairly regular way with changes in the electronic nature of the leaving group, the fraction of 2-methyl-2-pentene and ratio of trans-to cis-4-methyl-2-pentene for the most part increasing with increasing electron withdrawal. The E2 reactions in 25% t-butanol – dimethyl sulfoxide produce trans- and cis-4-methyl-2-pentene in ratios (20 to 35) considerably higher than those in an equilibrium mixture (ca. 6).The results are discussed in terms of recent views on the E2 transition state.

Effect of Medium on Reactivity for Alkaline Hydrolysis of p-Nitrophenyl Acetate and S-p-Nitrophenyl Thioacetate in DMSO-H2O Mixtures of Varying Compositions: Ground State and Transition State Contributions

2021 ◽  
Author(s):  
Ik-Hwan Um ◽  
Seungjae Kim
Keyword(s):  
Transition State ◽  
Alkaline Hydrolysis ◽  
Ground State ◽  
Rate Constants ◽  
Kinetic Data ◽  
Reaction Medium ◽  
Stepwise Mechanism ◽  
Rate Determining Step ◽  
Leaving Group ◽  
Hydrolysis Of

Second-order rate constants (kN) for reactions of p-nitrophenyl acetate (1) and S-p-nitrophenyl thioacetate (2) with OH‒ have been measured spectrophotometrically in DMSO-H2O mixtures of varying compositions at 25.0 ± 0.1 oC. The kN value increases from 11.6 to 32,800 M‒1s‒1 for the reactions of 1 and from 5.90 to 190,000 M‒1s‒1 for those of 2 as the reaction medium changes from H2O to 80 mol % DMSO, indicating that the effect of medium on reactivity is more remarkable for the reactions of 2 than for those of 1. Although 2 possesses a better leaving group than 1, the former is less reactive than the latter by a factor of 2 in H2O. This implies that expulsion of the leaving group is not advanced in the rate-determining transition state (TS), i.e., the reactions of 1 and 2 with OH‒ proceed through a stepwise mechanism, in which expulsion of the leaving group from the addition intermediate occurs after the rate-determining step (RDS). Addition of DMSO to H2O would destabilize OH‒ through electronic repulsion between the anion and the negative-dipole end in DMSO. However, destabilization of OH‒ in the ground state (GS) is not solely responsible for the remarkably enhanced reactivity upon addition of DMSO to the medium. The effect of medium on reactivity has been dissected into the GS and TS contributions through combination of the kinetic data with the transfer enthalpies (ΔΔHtr) from H2O to DMSO-H2O mixtures for OH‒ ion.

Octahedral cobalt(III) complexes of the chloropentanimine type. XXX. The thallium(III)-induced aquation of some cis-Halogeno(amine)bis(ethylenediamine)cobalt(III) cations in aqueous solution

1973 ◽  
Vol 26 (6) ◽  
pp. 1235 ◽  
Author(s):  
SC Chan ◽  
SF Chan
Keyword(s):  
Aqueous Solution ◽  
Rate Constants ◽  
Activation Parameters ◽  
Second Order ◽  
Alternative Possibility ◽  
Order Rate ◽  
Leaving Group ◽  
Activated Complex

The second-order rate constants for the thallium(III)-induced aquation of cis-[Co(en)2(RNH2)Cl]2+ cations, where R is H, Me, Et, Prn, and Pri, have been measured in aqueous solution over a range of temperatures, and the activation parameters calculated. The kinetic results are discussed in terms of a rapid pre-equilibrium formation of an activated complex Co-Cl-Tl, followed by a simple rate-determining aquation in which TlCl2+ acts as the leaving group, although the alternative possibility of a rate-determining attack by Tl3+ cannot be excluded. In the case of R = H, the investigations have been extended to the corresponding bromo cation which reacts some 50 times faster than its chloro analogue.

The Hydrolysis of Bis(2-chloroethyl) Sulfide (Sulfur Mustard) in Aqueous Mixtures of Ethanol, Acetone and Dimethyl Sulfoxide

1993 ◽  
Vol 46 (3) ◽  
pp. 293 ◽  
Author(s):  
RI Tilley
Keyword(s):  
Transition State ◽  
Dimethyl Sulfoxide ◽  
Rate Constants ◽  
Charge Separation ◽  
Sulfur Mustard ◽  
Transition States ◽  
Aqueous Mixtures ◽  
Sulfide Sulfur ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of

The rate of hydrolysis of bis (2-chloroethyl) sulfide (sulfur mustard) in aqueous mixtures of ethanol, acetone and dimethyl sulfoxide has been measured and compared with previously reported values. Rate constants in water at 25°C for the two consecutive hydrolysis reactions undergone by sulfur mustard were estimated to be (2.93�0.15)×10-3 and (3.87�0.14)×10-3 s-1. Charge separation of 0.42 in the transition states was indicated together with significant solvation of the positive end of the transition state dipoles.

Structure-reactivity correlations in the reaction of 2,4-dinitrophenyl X-substituted benzoates with alicyclic secondary amines

1999 ◽  
Vol 77 (5-6) ◽  
pp. 659-666 ◽  
Author(s):  
Ik-Hwan Um ◽  
Ji-Sook Min ◽  
Hye-Won Lee
Keyword(s):  
Rate Constants ◽  
Second Order ◽  
Secondary Amines ◽  
Electronic Nature ◽  
Order Rate ◽  
Rate Determining Step ◽  
Acyl Substituent ◽  
Plot Structure ◽  
Rate Limiting

Apparent second-order rate constants (kapp) have been measured spectrophotometrically for the reaction of 2,4-dinitrophenyl X-substituted benzoates with a series of alicyclic secondary amines in H2O containing 20 mol% DMSO at 25°C. The microconstants involved in the reaction (k-1/k2, k1, and k1k2/k-1) have also been calculated. The magnitude of kapp, k1, and k1k2/k-1 values increases with increasing amine basicity and with increasing acid strengthening ability of the acyl substituent X. The k-1/k2 value decreases from ca. 6.5 to 0.3 with increasing the amine basicity, but remains almost constant upon changing the acyl substituent X for a given amine, indicating that the rate-determining step is governed by the basicity of amine but not by the electronic nature of the acyl substituent X. The Brønsted-type plots for kapp show a break at pKa = 9.1, supporting the assumption that a change in the rate-determining step occurs from rate-limiting breakdown to formation of the addition intermediate as amine basicity increases. The corresponding Brønsted-type plots for k-1/k2, k1, and k1k2/k-1 are linear but their β values are different. σ+ constants show better correlation with log kapp, log k1 and log k1k2/k-1 for the reaction with low basic amines (pKa < 9.1), while σ constants exhibit better correlation for the reaction with highly basic amines (pKa > 9.1). The magnitude of ρ1 is identical to that of ρapp and ρeq for a given amine.Key words: aminolysis, Brønsted-type plot, structure-reactivity correlations, rate-determining step.

Primary isotope effects and mechanism of base initiated β-elimination reactions of di-(p-nitrophenyl)fluoroethanes

1977 ◽  
Vol 55 (10) ◽  
pp. 1696-1700 ◽  
Author(s):  
Jan Kurzawa ◽  
Kenneth T. Leffek
Keyword(s):  
Transition State ◽  
Rate Constants ◽  
Sodium Methoxide ◽  
Isotope Effects ◽  
Activation Parameters ◽  
Second Order ◽  
Order Rate ◽  
Elimination Reactions

The second-order rate constants have been determined for the β-elimination reactions of 2,2-di-(p-nitrophenyl)-1,1,1-trifluoroethane, 2,2-di-(p-nitrophenyl)-1-fluoroethane, and their β-deuterated analogues with sodium methoxide in methanol. The primary isotope effects and activation parameters for these reactions are reported. It is suggested that the trifluoro-compound reacts via the pre-equilibrium carbanion mechanism (ElcB)R and that the monofluoro compound follows the E2 mechanism via a carbanion-like transition state.

Rates of Reaction of Nickel (II) with Terpyridine in Dimethyl Sulfoxide

1972 ◽  
Vol 50 (3) ◽  
pp. 402-411 ◽  
Author(s):  
Patricia A. Cock ◽  
C. E. Cottrell ◽  
R. K. Boyd
Keyword(s):  
Dimethyl Sulfoxide ◽  
Rate Constants ◽  
Second Order ◽  
Dmso Solution ◽  
Substitution Reactions ◽  
Order Rate ◽  
Nickel Species

The rates at which 2,2′,2″-terpyridine reacts with nickel(II) ion to form the monoligand–nickel(II) and the bisligand–nickel(II) complexes were determined in DMSO solution. Ni(terpy)Cl2 was isolated, and used to study the rate of formation of bis complex. The second-order rate constants were found to parallel the rates of DMSO exchange, determined using n.m.r. techniques, from the respective paramagnetic nickel species. Attempts were made to relate the results to the generally accepted "dissociative" pathways for this class of substitution reactions.

The kinetics and mechanism of the reaction between nickel(II) and dithiocarbamate ions in dimethyl sulfoxide. Evidence for the ID mechanism for a bidentate uninegative ligand

1978 ◽  
Vol 31 (12) ◽  
pp. 2581 ◽  
Author(s):  
PJ Nichols ◽  
MW Grant
Keyword(s):  
Fourier Transform ◽  
Ionic Strength ◽  
Dimethyl Sulfoxide ◽  
Excellent Agreement ◽  
Rate Constants ◽  
Second Order ◽  
Kinetics And Mechanism ◽  
First Order ◽  
Temperature Dependences ◽  
Mechanism Of The Reaction

13C Fourier-transform N.M.R. has been used to measure the rate of exchange of dimethyl sulfoxide with hexakis(dimethyl sulfoxide)nickel(II) cation. The parameters obtained, kex(25°C)(9.8�4.6) × 103 s-1, ΔH‡ 50�2 kJ mol-1 and ΔS‡ 0�4 J K-1 mol-1, are in excellent agreement with those of the most recent 1H N.M.R. study. The reaction between Ni(Me2SO)62+ and diethyldithiocarbamate (dtc-) gives only Ni(dtc)2. When dtc- is in excess, the rate of formation of Ni(dtc)2 is first order in Ni2+ and dtc-. The ionic-strength and temperature dependences of the second-order rate constants are consistent with the rate-determining formation of an unstable Ni(dtc)+ complex by an ID mechanism.

Pyrolysis of aryl azides. III. Steric and electronic effects upon reaction rate

1975 ◽  
Vol 28 (10) ◽  
pp. 2147 ◽  
Author(s):  
LK Dyall
Keyword(s):  
Transition State ◽  
Rate Constants ◽  
Reaction Rate ◽  
Steric Effects ◽  
Electronic Effects ◽  
Aryl Azides ◽  
Phenyl Azide ◽  
Methyl Group ◽  
First Order ◽  
Ortho Substituent

First-order rate constants have been measured for the pyrolysis of 15 phenyl azides in decalin solution. The rate for phenyl azide is increased only slightly by all para and many ortho substituents; in these cases Eact and ΔSact values are related linearly. ��� The very large rate increases when the ortho substituent is phenylazo, nitro, acetyl or benzoyl cannot be from steric or normal electronic effects and therefore identify a specific involvement of these groups in the transition state. This rate enhancement is reduced to scarcely significant levels by a 6-chloro or 6-methyl group in 2- nitrophenyl azide, but not by a 6-nitro group. These results raise doubts about recent claims1 to establish mechanism by measuring polar effects on rates of pyrolysis of azides in which steric effects might also operate.

Styrene Forming Elimination Reaction from β-Phenylethylphosphonium Salts+

1983 ◽  
Vol 38 (1) ◽  
pp. 115-116 ◽  
Author(s):  
S. Alunni ◽  
G. Giulietti
Keyword(s):  
Rate Constants ◽  
Second Order ◽  
Elimination Reaction ◽  
Order Rate ◽  
Leaving Group

β-Phenylethylphosphonium salts in RO-/ROH give styrene in amount depending on the steric requirements of the nucleophile and of the salt. The % of styrene formed increases from 22.9 with leaving group PPH3 to 85.0 with leaving group P(<-BU)3 in t-BuOK/t-BuOH. Second order rate constants at 30 °C in t-BuOK/t-BuOH are 1.1 · 10-2lm-1s-1 with leaving group P(n-Bu)3 and 0.96- 10-2 lm-1s-1 with leaving group P (cyclohexyl)3. The data are consistent with a mechanism of β-elimination.

Hydride transfer reactions. Substituent effects in oxidation of N-benzylacridans by π acceptors

1983 ◽  
Vol 61 (11) ◽  
pp. 2544-2551 ◽  
Author(s):  
Allan K. Colter ◽  
Charles C. Lai ◽  
Terry W. Williamson ◽  
Raymond E. Berry
Keyword(s):  
Transition State ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Substituent Effects ◽  
Second Order ◽  
Face To Face ◽  
Order Rate ◽  
Linear Free Energy ◽  
Donor And Acceptor ◽  
Kinetics Of

The kinetics of oxidation of a series of eight N-(substituted benzyl)acridans (3, NBA's) by 1,4-benzoquinone (BQ), p-chloranil (CA), 2,3-dicyano-1,4-benzoquinone (DCBQ), 7,7,8,8-tetracyanoquinodimethane (TCNQ), and tetracyanoethylene (TCNE) in acetonitrile (AN) and by BQ in 50:50 (v/v) AN-water were measured at 25 °C. Equilibrium constants for pseudobase formation, [Formula: see text], from the corresponding acridinium ions (4) were measured in water at 25 °C. Hammett correlations of the second-order rate constants for reaction of the NBA's without ortho substitutents (3a–e) led to ρ values of −0.29 (BQ, AN), −0.55 (CA), −0.56 (DCBQ), −0.64 (TCNQ), −0.41 (TCNE), and −0.47 (BQ, 50:50 AN–water). The second-order rate constants for 3a–e also give good linear free energy correlations with the [Formula: see text] values of 4a–e. These correlations and the [Formula: see text] values for the ortho-substituted acridinium ions (4f, g, h) are used to calculate rate constants for oxidation of the corresponding ortho-substituted NBA's (3f, g, h). The rate constants calculated in this way are 4.7 to 6.6 times and 6.4 to 12 times larger, respectively, than the observed rate constants for N-(2,4,6-trimethylbenzyl) and N-(2,6-dichlorobenzyl)acridan (3g and h). The variations in ρ values are attributed mainly to differences in the amount of electrostatic stabilization in the transition state resulting from differences in the separation of donor and acceptor and the degree of delocalization of the negative charge. The rate retarding effect of a pair of ortho substituents is attributed to sterie effects in a preferred face-to-face transition state.

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