Kinetic solvent isotope effect, solvent reorganization, and the SN1–SN2 mechanism

1969 ◽  
Vol 47 (18) ◽  
pp. 3397-3404 ◽  
Author(s):  
L. Treindl ◽  
R. E. Robertson ◽  
S. E. Sugamori
Keyword(s):  
Heat Capacity ◽  
Probable Mechanism ◽  
Activation Process ◽  
Solvent Structure ◽  
Butyl Chloride ◽  
Solvent Isotope Effect ◽  
Mechanism Of Reaction ◽  
Wide Range ◽  
Two Temperatures ◽  
Solvent Isotope

The temperature dependence of the rates of solvolysis have been determined in D2O for t-butyl chloride, 2,2-dibromopropane, 2-bromo-2-chloropropane, and 2-chloro-2-methyl propyl methyl ether, and corresponding values of ΔH≠, ΔS≠, and ΔCp≠ are derived. Values of ΔH≠ and ΔS≠ from the solvolysis of seven other halides and two benzenesulfonates have been estimated from rate determinations at two temperatures in D2O.A comparison of these values with terms from corresponding experiments in H2O provides values of δIΔG≠, δIΔH≠, and δIΔS≠ characterizing the kinetic solvent isotope effect.While δIΔG≠ appears to have about the same value for a wide range of halides of different structure irrespective of the probable mechanism of reaction, systematic differences in δIΔH≠ and δIΔS≠ differentiate those reacting by an SN2 mechanism from those reacting by an SN1 mechanism. This difference is in the direction suggesting a loosening of solvent structure in the activation process in agreement with indications obtained from the corresponding values of the heat capacity of activation.

THE ACTIVATION PROCESS IN SOLVOLYSIS

1964 ◽  
Vol 42 (7) ◽  
pp. 1707-1711 ◽  
Author(s):  
R. E. Robertson
Keyword(s):  
Activation Energy ◽  
Heat Capacity ◽  
Transition State ◽  
Isotope Effect ◽  
Activation Process ◽  
Solvent Isotope Effect ◽  
Apparent Heat Capacity ◽  
Structural Nature ◽  
Solvent Isotope

The structural nature of water is a major factor in determining the solvent isotope effect and the apparent heat capacity of activation for solvolysis. The consequences of this assumption are examined for the SN2 mechanism in terms of solvation changes at the transition state and the probable make-up of the activation energy.

The Hydrolysis of Disubstituted Alkyl Phosphorochloridates and N,N,N′,N′-Tetra-stibstituted Phosphorodiamidic Chlorides in Water and Deuterium Oxide: Heat Capacity of Activation and Kinetic Solvent Isotope Effects

1973 ◽  
Vol 51 (4) ◽  
pp. 597-603 ◽  
Author(s):  
E. C. F. Ko ◽  
R. E. Robertson
Keyword(s):  
Heat Capacity ◽  
Thermodynamic Parameters ◽  
Alkyl Group ◽  
Deuterium Oxide ◽  
Isotope Effects ◽  
Potential Relationship ◽  
Mechanism Of Reaction ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Solvent Isotope Effects

The pseudo-thermodynamic parameters, ΔH≠, ΔS≠, and ΔCp≠ and the kinetic solvent isotope effects have been determined for the three alkyl-phosphorochloridates, where the alkyl group is ethylisopropyl and n-propyl; for tetra-methyl and tetra-ethyl phosphorodiamidic chlorides; the di-n-propyl and di-isopropyl analog, the di(isopropylmethylcarbinyl)phosphorochloridate and the tetra-ethylthiophosphorodiamidic chloride. These compounds have a potential relationship to compounds used as insecticides and as polymers. The mechanism of reaction is discussed on the basis of these data.

Solvolysis of sulphonyl halides. V. Hydrolysis and deuterolysis of methanesulphonyl chloride

1970 ◽  
Vol 23 (12) ◽  
pp. 2427
Author(s):  
ML Tonnet ◽  
AN Hambly
Keyword(s):  
Transition State ◽  
Thermodynamic Parameters ◽  
Isotope Effect ◽  
Large Reduction ◽  
Butyl Chloride ◽  
Solvent Isotope Effect ◽  
Initial State ◽  
Solvent Isotope ◽  
Hydrolysis Of

The values of the thermodynamic parameters of activation have been determined for the solvolysis of methanesulphonyl chloride in H2O and D2O and their mixtures with moderate amounts of dioxan. Some of the data are not in agreement with the postulate that the kinetic solvent isotope effect and the maximum in the rate of solvolysis produced by the addition of dioxan are due to changes in the initial state of the reacting system rather than to changes in the transition state. The addition of dioxan does not produce a large reduction in the solvent isotope effect as reported for the hydrolysis of t-butyl chloride and predicted to be general. The relative rates of solvolysis in mixtures of H2O and D2O are not in agreement with the analysis of such reactions by Swain and Thornton.

The Hydrolysis of t-Butyl Chloride in Aquo-Organic Mixtures: Heat Capacity of Activation and Solvent Structure

1972 ◽  
Vol 50 (9) ◽  
pp. 1353-1360 ◽  
Author(s):  
R. E. Robertson ◽  
S. E. Sugamori
Keyword(s):  
Heat Capacity ◽  
Temperature Dependence ◽  
High Water ◽  
Remarkable Difference ◽  
Solvent Structure ◽  
Butyl Chloride ◽  
Organic Mixtures ◽  
A Value ◽  
Polar Solutes ◽  
Hydrolysis Of

The temperature dependence of the rate of solvolysis of t-butyl chloride in mixtures of tetrahydrofuran and of acetonitrile in water have been determined. In the high-water range both minor co-solvents lead to a reduction in the value of ΔH≠ similar to that found previously where alcohol was the co-solvent. However, a remarkable difference in the values of [Formula: see text] across the same concentration range reflected a difference in the effect of these two co-solvents on the structural properties of the several solvent media. Where tetrahydrofuran or alcohols are the minor co-solvent, [Formula: see text] becomes much more negative until that concentration is reached where the quasi-aqueous structure collapses. Where acetonitrile is the minor co-solvent [Formula: see text] becomes more positive relative to the value found for hydrolysis in water until a value of about −40 cal deg−1 mol−1 is reached. The implication of these findings concerning the nature of solvation of weakly polar solutes in such mixtures is discussed.

SOLVOLYSIS IN LIGHT AND HEAVY WATER: V. EFFECT OF DIOXANE ON THE SOLVENT ISOTOPE EFFECT WITH t-BUTYL CHLORIDE

1963 ◽  
Vol 41 (8) ◽  
pp. 2118-2120 ◽  
Author(s):  
Wm. G. Craig ◽  
Leo Hakka ◽  
P. M. Laughton ◽  
R. E. Robertson
Keyword(s):  
Isotope Effect ◽  
Heavy Water ◽  
Butyl Chloride ◽  
Solvent Isotope Effect ◽  
Solvent Isotope

not available

The Mechanism for Hydrolysis of Primary Alkyl Chlorosulfates in Water. The Kinetic Solvent Isotope Effect and the Secondary Deuterium Isotope Effect

1972 ◽  
Vol 50 (3) ◽  
pp. 434-437 ◽  
Author(s):  
E. C. F. Ko ◽  
R. E. Robertson
Keyword(s):  
Isotope Effect ◽  
Sulfonyl Chloride ◽  
Alkyl Halides ◽  
Activation Process ◽  
Deuterium Isotope Effect ◽  
Solvent Isotope Effect ◽  
Temperature Coefficients ◽  
Enthalpy Of Activation ◽  
Solvent Isotope ◽  
Hydrolysis Of

The temperature coefficients of the enthalpy of activation [Formula: see text] for the hydrolysis of the three chlorosulfates, methyl, ethyl, and β-chloro, are shown to have values of −50,−55, and −60 cal deg−1 mol−1; values in the same range as previously reported for the hydrolysis of the sulfonyl chlorides. The corresponding value for the β-methoxy isomer was −40 cal deg−1 mol−1, about the same as found for the p-methoxybenzenesulfonyl chloride. The kinetic solvent isotope effect, however, was significantly lower than reported for the sulfonyl chloride series, being about the same as found for the hydrolysis of the alkyl halides. While some degree of nucleophilic overlap is probably required in the activation process, the requirement here is reduced to about the same level as that for the primary halides, and there is no need to postulate a different mechanism on passing from the methyl to the ethyl member of the series, confirming the earlier conclusion of Buncel and Millington.

Vinyl ether hydrolysis XXVIII. The mechanism of reaction of methyl α-(2,6-dimethoxyphenyl)vinyl ether

1993 ◽  
Vol 71 (1) ◽  
pp. 38-41 ◽  
Author(s):  
J. Jones ◽  
A. J. Kresge
Keyword(s):  
Vinyl Ether ◽  
Nucleophilic Attack ◽  
Tracer Study ◽  
Solvent Isotope Effect ◽  
Methyl Group ◽  
Hydronium Ion ◽  
Mechanism Of Reaction ◽  
Acid Catalyzed ◽  
Solvent Isotope ◽  
Hydrolysis Of

The acid-catalyzed hydrolysis of methyl α-(2,6-dimethoxyphenyl)vinyl ether in aqueous solution at 25 °C occurs with the hydronium ion catalytic coefficient [Formula: see text] and gives the solvent isotope effect [Formula: see text] this indicates that reaction occurs by rate-determining proton transfer from the catalyst to the substrate to generate an alkoxycarbocation intermediate. An oxygen-18 tracer study shows further that, despite the steric hindrance provided by its two ortho substituents, this cation then reacts by addition of water to the cationic carbon atom to generate a hemiacetal, and not by nucleophilic attack of water on the methyl group remote from the carbocationic center:[Formula: see text]

Solvent reorganization for hydrolysis with hydrogen participation

1969 ◽  
Vol 47 (24) ◽  
pp. 4599-4605 ◽  
Author(s):  
Y. Inomoto ◽  
R. E. Robertson ◽  
G. Sarkis
Keyword(s):  
Acetic Acid ◽  
Isotope Effect ◽  
Activation Process ◽  
Solvent Isotope Effect ◽  
Butyl Bromide ◽  
Rate Of Hydrolysis ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Reaction In Water

A study of the rates of hydrolysis of 3-Me-2-butyl bromide and methanesulfonate in water leads to values of ΔCp≠ of −80 and −40 cal deg−1 mole−1, respectively. The product was about 85–95 % t-pentanol, the remainder being olefin. The value of ΔCp≠ for the solvolysis of the methanesulfonate in D2O was −44 cal deg−1 mole−1. The kinetic solvent isotope effect (k.s.i.e.) for the latter was unusually low (k.s.i.e. = 1.047 at 5 °C and 1.025 at 25 °C). Deuteration at C-3 led to a reduction in the rate of hydrolysis by a factor of about 2.25. This is consistent with an activation process involving "hydrogen participation" as previously reported by Winstein and Takahashi for solvolysis of the corresponding tosylate in acetic acid. In contrast to the latter work, the reaction in water appears to be uncomplicated.

scholarly journals Kinetics and Mechanism of the Oxidation of α-Hydroxy Carboxylic Acids by Bromine

1973 ◽  
Vol 28 (7-8) ◽  
pp. 450-453 ◽  
Author(s):  
Kalyan K. Banerji
Keyword(s):  
Isotope Effect ◽  
Hydroxy Acid ◽  
Kinetic Isotope Effect ◽  
Activation Parameters ◽  
Probable Mechanism ◽  
Molecular Bromine ◽  
Solvent Isotope Effect ◽  
First Order ◽  
Kinetic Isotope ◽  
Solvent Isotope

The oxidation of glycollic, lactic, u-hydroxybutyric, and 2-phenyllactic acids by aqueous bromine has been studied. The reaction is of first order with respect to the oxidant and the anion of the hydroxy acid respectively. The active oxidising species is molecular bromine. The oxidation of α,α-dideuterioglycollic acid indicated a kinetic isotope effect, kH/kD=4.62 at 25°C. The reaction does not show any appreciable solvent isotope effect. The activation parameters arc evaluated. A probable mechanism has been suggested.

Sign in / Sign up

Export Citation Format

Share Document