Kinetic deuterium isotope effect in the reaction of methyl iodide with thiosulfate ion in aqueous solution

1970 ◽  
Vol 48 (9) ◽  
pp. 1452-1455
Author(s):  
Alfred V. Willi ◽  
Chong Min Won
Keyword(s):  
Aqueous Solution ◽  
Gas Phase ◽  
Isotope Effect ◽  
Methyl Iodide ◽  
Isotope Effects ◽  
Force Constants ◽  
Deuterium Isotope Effect ◽  
Model Calculations ◽  
Bending Force ◽  
Reaction Vessels

The kinetic deuterium isotope effect in the reaction of methyl iodide with thiosulfate ion in aqueous solution has been determined as follows: kH/kD (per 3D) = 0.966 (+0.02°), 0.968 (+10.00°), 0.970 (+19.98°). Kinetic experiments have been carried out in reaction vessels with no gas phase. The experimental data are compared with results of model calculations of isotope effects from force constants. Excellent agreement between experimental and calculated isotope effects may be obtained with the following values of the transition state bending force constants: fHCI = 0.295 mdyn Å, fHCS = 0.300 to 0.320 mdyn Å. These values are equal to 50–65% of the corresponding bending force constants in stable molecules.

scholarly journals Berechnung kinetischer Isotopeneffekte für die Reaktion von Methyljodid mit Hydroxid-Ion

1966 ◽  
Vol 21 (9) ◽  
pp. 1385-1390 ◽  
Author(s):  
A. V. Willi
Keyword(s):  
Experimental Data ◽  
Transition State ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Force Constants ◽  
Linear Functions ◽  
Bending Force ◽  
Small Influence ◽  
Carbon Isotope Effect ◽  
Secular Equations

Kinetic carbon-13, deuterium, and oxygen-18 isotope effects are calculated from force constants for the SN2 reaction of CH3I with OH-. The secular equations for the vibrational frequencies of reactants and transition states are solved on an IBM 7094 computer. Values for 7 force constants of the planar CH3 moiety in the transition state (with an sp2 atom) are obtained by comparison with suitable stable molecules. The stretching force constants ƒCO = ƒ11, ƒCI = ƒ22, and ƒ12 in the transition state are chosen as linear functions of x, the degree of bond making and bond breaking, with the aid of eqs. (1) and (2).The carbon isotope effect as a function of x exhibits a flat maximum near x=0.6. If the bending force constants ƒHCO and ƒHCI are kept constant, k12/k13 is significantly lower than its maximum value only for values of x ≦ 0.3 and x ≧ 0.8. There is only a small influence of x on the deuterium isotope effect, kH/kD (compare rates of CH3I and CD3I). However, kH/kD) is strongly dependent on ƒHCO and ƒHCI . The oxygen-18 isotope effect decreases with increasing x. Experimental data of the D isotope effect — if they were available — could be used to adjust the bending force constants ƒHCO and ƒHCI (— or to adjust ƒHCO if ƒHCI is held constant). The degree of unsymmetry of the transition state could then be estimated with the aid of the C isotope effect. Experimental data of the O isotope effect would supply information on the direction of the unsymmetry — which is needed for a distinction between 2 possible values of x —. There is approximate agreement between the calculated and the experimental temperature dependence of the carbon-13 isotope effect.

Berechnung kinetischer Isotopeneffekte für die Reaktion von Methyljodid mit Cyanid-Ion

1966 ◽  
Vol 21 (9) ◽  
pp. 1377-1384
Author(s):  
A. V. Willi
Keyword(s):  
Transition State ◽  
Secular Equation ◽  
Isotope Effects ◽  
Force Constants ◽  
Bond Breaking ◽  
Bending Force ◽  
A Value ◽  
Order Of Magnitude ◽  
Deuterium Isotope Effects ◽  
The Difference

Kinetic carbon-13 and deuterium isotope effects are calculated for the SN2 reaction of CH3I with CN-. The normal vibrational frequencies of CH3I, the transition state I · · · CH3 · · · CN, and the corresponding isotope substituted reactants and transition states are evaluated from the force constants by solving the secular equation on an IBM 7094 computer.Values for 7 force constants of the planar CH3 moiety in the transition state (with an sp2 C atom) are obtained by comparison with suitable stable molecules. The stretching force constants related to the bonds being broken or newly formed (fCC, fCC and the interaction between these two stretches, /12) are chosen in such a way that either a zero or imaginary value for νʟ≠ will result. Agreement between calculated and experimental methyl-C13 isotope effects (k12/ k13) can be obtained only in sample calculations with sufficiently large values of f12 which lead to imaginary νʟ≠ values. Furthermore, the difference between fCI and fCC must be small (in the order of 1 mdyn/Å). The bending force constants, fHCI and fHCC, exert relatively little influence on k12/k13. They are important for the D isotope effect, however. As soon as experimental data on kH/kD are available it will be possible to derive a value for fHCC in the transition state if fHCI is kept constant at 0.205 mdynA, and if fCI, fCC and f12 are held in a reasonable order of magnitude. There is no agreement between experimental and calculated cyanide-C13 isotope effects. Possible explanations are discussed. — Since fCI and fCC cannot differ much it must be concluded that the transition state is relatively “symmetric”, with approximately equal amounts of bond making and bond breaking.

Ruthenium catalysed oxidation of cyclohexanol

1982 ◽  
Vol 35 (6) ◽  
pp. 1245 ◽  
Author(s):  
P Becker ◽  
JK Beattie
Keyword(s):  
Aqueous Solution ◽  
Isotope Effect ◽  
Phosphate Buffer ◽  
Hydride Transfer ◽  
Deuterium Isotope Effect ◽  
Rate Law ◽  
Alkaline Aqueous Solution ◽  
Catalysed Oxidation

The oxidation of cyclohexanol by ferricyanide in alkaline aqueous solution is catalysed by micromolar concentrations of K3RuCl6. The rate law at 25.0�C in pH 11.9 phosphate buffer containing 0.50 M NaCl is -d[FeIII]/dt = [Ru](2klk2[alcohol][FeIII])/(2kl[alcohol] + k2[FeIII]) with kl 12 � 2 mol-1 1. s-1 and k2 (2.5 � 0.2) × 102 mol-1 1. s-1. A deuterium isotope effect of about 4 is observed when (D12)cyclohexanol is used. A mechanism consistent with these observations involves reduction of the RuIII catalyst by hydride transfer from the alcohol followed by reoxidation by ferricyanide to the original RulIII state.

2,4-Diazapentadienes. II. A Carbanion Cyclization

1972 ◽  
Vol 50 (5) ◽  
pp. 678-689 ◽  
Author(s):  
D. H. Hunter ◽  
S. K. Sim
Keyword(s):  
Isotope Effect ◽  
Solvent Effects ◽  
Isotope Effects ◽  
Substituent Effects ◽  
Deuterium Exchange ◽  
Hydrogen Deuterium Exchange ◽  
Deuterium Isotope Effect ◽  
Potassium Methoxide ◽  
Proton Shift ◽  
Hydrogen Deuterium

The mechanism of the cyclization and 1,3-proton shift of 1,3,5-triaryl-2,4-diaza-1,3-pentadienes (1) catalyzed by phenyllithium and by potassium methoxide–methanol has been studied. On the basis of substituent effects, hydrogen–deuterium exchange, isotope effects, and solvent effects, it was deduced that both the cyclization and prototropy involve a common W-shaped carbanion which rapidly cyclizes. A kinetic deuterium isotope effect of 2 was calculated for protonation of this intermediate carbanion in methanol.

Correlation of isotope effects in substitution reactions with nucleophilicities. Secondary α-deuterium isotope effect in the iodide-131 exchange of methyl-d3 iodide

1967 ◽  
Vol 45 (18) ◽  
pp. 2023-2031 ◽  
Author(s):  
Stanley Seltzer ◽  
Andreas A. Zavitsas
Keyword(s):  
Nucleophilic Substitution ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Substitution Reactions ◽  
Deuterium Isotope Effect ◽  
Nucleophilic Substitution Reactions ◽  
Leaving Group ◽  
The Difference

The secondary α-deuterium isotope effect in iodide-131 exchange of methyl-d3 iodide is kH/kD = 1.05 ± 0.01 in methanol and 1.10 ± 0.04 in water at 20°. A correlation of secondary α-deuterium and 13C effects, in bimolecular nucleophilic substitution reactions, with the difference of E values between nucleophile and leaving group is presented.

Réactions d'addition nucléophiles sur les cétones. Mise en évidence d'un effet directionnel d'origine stérique dans l'effet isotopique secondaire du deutérium

1980 ◽  
Vol 58 (1) ◽  
pp. 55-59 ◽  
Author(s):  
Bernard Boyer ◽  
Gérard Lamaty ◽  
Jean-Pierre Roque ◽  
Patrick Geneste
Keyword(s):  
Kinetic Study ◽  
Isotope Effect ◽  
Carbonyl Compounds ◽  
Isotope Effects ◽  
Reaction Process ◽  
Addition Reactions ◽  
Deuterium Isotope Effect ◽  
Directional Effect ◽  
Sulfite Ions ◽  
Process Journal

A kinetic study of the addition reactions of borohydride and sulfite ions and of hydroxylamine to a number of stereospecifically deuterated carbonyl compounds (3,3,5,5-tetramethyl cyclohexanone, 7,7-d2-bicyclo[2,2,1]-2-bornanone) leads to the observation of a distant secondary deuterium isotope effect. The results obtained reveal the intervention of a directional effect in the steric origin of these isotope effects. In particular, this study shows the importance of the orientation of the vibrations brought into play by a C—D bond during the reaction process. (Journal translation)

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