Kinetics of Proton Transfer Reactions of Carbon Acids. IV. Primary Deuterium Isotope Effect in the Reaction of Di-(4-nitrophenyl)methane-d2 with t-Butoxide

Kim, Jae-Hang; Leffek, Kenneth T.

doi:10.1139/v74-092

Cited by 9 publications

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References 3 publications

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“…It may be seen that the rate constants and activation parameters in solvents containing 20, I I 50 and 80% v/v toluene in t-butyl alcohol form a series with the results in 10% v/v toluene-t-butyl alcohol reported earlier (3), in which the changes in these reaction characteristics are smooth. The rate constants decrease as the toluene content of the solvent is increased and are very small for solvents above 80% toluene.…”

supporting

confidence: 62%

Kinetics of Proton Transfer Reactions of Carbon Acids. V. Variation of Primary Deuterium Isotope Effect with Solvent Composition for the Reaction of Di-(4-nitrophenyl)methane with t-Butoxide in t- Butyl Alcohol–Toluene Mixtures

Jarczewski¹,

Pruszyński²,

Leffek³

1975

Can. J. Chem.

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ARNOLD JARCZEWSKI, PRZEMYSLAW PRUSZYNSKI, and KENNETH T. LEFFEK. Can. J. Chem. 53, 1176 (1975).The second-order rate constants, activation parameters, and primary deuterium isotope effects are reported for the proton transfer reaction from di-(4-nitropheny1)methane to t-butoxide ion in a series of solvents containing varying amounts of toluene in t-butyl alcohol. Increasing toluene content in the solvent decreases the rate constant and increases the enthalpy of activation, while the entropy of activation becomes less negative. The isotope rate ratio kH/kD increases from 7.3 in 10% v/v toluene to 9.4 in 50% vv/ toluene at 25 "C, corresponding to a change in (AHD* -AHH*) from 0.46 to 1.0 kcal mol-' and a change in (AS,* -A S H f ) from -2.4 to -1.1 cal mol-' deg-'. It is suggested that the negative values for (ASDf -A S H f ) are due to a time lag for solvent reorganization relative to the proton transfer.ARNOLD JARCZEWSKI, PRZEMYSLAW PRUSZYNSKI et KENNETH T. LEFFEK. Can. J. Chem. 53, 1176 (1975).On rapporte les constantes de vitesse du second ordre. les parametres d'activation et les effets isotopiques primaires du deuterium pour le transfert de proton lors de la rtaction du di-(nitro-4 phtny1)methane avec l'ion t-butylate dans une strie de solvants contenant des quantitts variables de toluene dans I'alcool t-butylique. L'augmentation du contenu en toluene dans le solvant diminue la vitesse de rtaction et augmente l'enthalpie d'activation alors que I'entropie d'activation devient moins ntgative. A 25 "C, le rapport des vitesses kH/kD augmente de 7.3 lorsque I'on a 10% vv/ de toluene a 9.4 lorsque l'on a 50% vv/ de toluene; cette variation correspond a un changement dans le (AHD* -AHH*) de 0.46 1.0 kcal mol-' et un changement dans (ASD* -ASH9) de -2.4 a -1.1 cal mol-I deg-l. On suggere que les valeurs negatives pour (ASD* -ASH*) sont principalement dues a un retard dans la rtorganisation du solvant par rapport a la vitesse du transfert du proton.[Traduit par le journal]

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confidence: 62%

Kinetics of Proton Transfer Reactions of Carbon Acids. V. Variation of Primary Deuterium Isotope Effect with Solvent Composition for the Reaction of Di-(4-nitrophenyl)methane with t-Butoxide in t- Butyl Alcohol–Toluene Mixtures

Jarczewski¹,

Pruszyński²,

Leffek³

1975

Can. J. Chem.

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“…The proton-transfer reactions of nitroalkanes have received a great deal of attention in the past half-century. − They are moderately strong C−H acids and the conjugate bases are often long-lived which coupled with strong absorbance bands in the visible region renders the kinetics readily studied by conventional techniques. The question of quantum mechanical tunneling during cleavage of the C−H bond in these compounds has been the topic of much discussion.…”

Section: Discussionmentioning

confidence: 99%

“…Numerous studies of the proton-transfer reactions of nitroalkanes with both neutral and anionic bases have been carried out over the past half-century. − The reactions are conveniently studied by spectrophotometry since the stable anionic products exhibit strong absorbance bands in the visible spectral region. The very large deuterium kinetic isotope effects (≅50) reported by Caldin and Mateo 7,8 for the reaction between 4-nitrophenylnitromethane (NPNM) with tetramethylguanidine (TMG), a strong organic base with an exchangeable N−H, in toluene were quickly challenged by two groups. ,, Reinvestigations of the reaction revealed that the results reported for the D-labeled acid are unreliable due to proton/deuteron (H/D) exchange and that KIE app was lowered to about 11 when the base was changed to (Me 2 N) 2 CND.…”

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confidence: 99%

Proton-Transfer Reactions between Nitroalkanes and Hydroxide Ion under Non-Steady-State Conditions. Apparent and Real Kinetic Isotope Effects

2001

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The kinetics of the proton-transfer reactions between 1-nitro-1-(4-nitrophenyl)ethane (NNPE(H(D))) and hydroxide ion in water/acetonitrile (50/50 vol %) were studied at temperatures ranging from 289 to 319 K. The equilibrium constants for the reactions are large under these conditions, ensuring that the back reaction is not significant. The extent of reaction/time profiles during the first half-lives are compared with theoretical data for the simple single-step mechanism and a 2-step mechanism involving initial donor/acceptor complex formation followed by unimolecular proton transfer and dissociation of ions. In all cases, the profiles for the reactions of both NNPE(H) and NNPE(D) deviate significantly from those expected for the simple single-step mechanism. Excellent fits of experimental data with theoretical data for the complex mechanism, in the pre-steady-state time period, were observed in all cases. At all base concentrations (0.5 to 5.0 mM) and at all temperatures the apparent kinetic isotope effects (KIE(app)) were observed to increase with increasing extent of reaction. Resolution of the kinetics into microscopic rate constants at 298 K resulted in a real kinetic isotope effect (KIE(real)) for the proton-transfer step equal to 22. Significant proton tunneling was further indicated by the temperature dependence of the rate constants for proton and deuteron transfers: KIE(real) ranging from 17 to 26, E(a)(D) -- E(a)(H) equal 2.8 kcal/mol, and A(D)/A(H) equal to 4.95.

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“…Many of the studies of proton tunneling in organic reactions have been concerned with proton transfer reactions of nitroalkanes, − and these reactions have been treated as simple reversible second-order reactions. Since we have shown 4 that the proton transfer reactions of a representative substrate in this series, 1-nitro-1-(4-nitrophenyl)ethane, with hydroxide take place by the complex mechanism some doubt arises as to whether the previous proton tunneling discussions have dealt with KIE real or with KIE app which cannot be equated to the latter for the proton transfer steps.…”

Section: Discussionmentioning

confidence: 99%

Proton Transfer Reactions of Methylanthracene Radical Cations with Pyridine Bases under Non-Steady-State Conditions. Real Kinetic Isotope Effect Evidence for Extensive Tunneling

2001

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The kinetics of the proton transfer reactions between the 9-methyl-10-phenylanthracene radical cation (MPA(+)(.)) with 2,6-lutidine were studied in acetonitrile-Bu(4)NBF(4) (0.1 M) using derivative cyclic voltammetry. Comparisons of extent of reaction-time profiles with theoretical data for both the simple single-step proton transfer and a mechanism involving the formation of a donor-acceptor complex prior to unimolecular proton transfer were made. The experimental extent of reaction-time profiles deviated significantly from those simulated for the single-step mechanism, while excellent fits of experimental to theoretical data, in the pre-steady-state period, for the complex mechanism were observed. In this time period, the apparent deuterium kinetic isotope effects (KIE(app)) were observed to vary significantly with the extent of reaction as predicted by the complex mechanism. Resolution of the apparent rate constants into the microscopic rate constants for the complex mechanism resulted in a real kinetic isotope effect (KIE(real)) equal to 82 at 291 K. Arrhenius activation parameters (252-312 K) for the reactions of MPA(+)(*) with 2,6-lutidine in acetonitrile-Bu(4)NBF(4) (0.1 M) revealed E(a)(D) - E(a)(H) equal to 2.89 kcal/mol and A(D)/A(H) equal to 2.09. In this temperature range, KIE(real) varied from 46 at the highest temperature to 134 at the lowest. The large KIE(real), along with the Arrhenius parameters, are indicative of extensive tunneling for the proton transfer steps.

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Kinetics of Proton Transfer Reactions of Carbon Acids. IV. Primary Deuterium Isotope Effect in the Reaction of Di-(4-nitrophenyl)methane-d₂ with t-Butoxide

Cited by 9 publications

References 3 publications

Kinetics of Proton Transfer Reactions of Carbon Acids. V. Variation of Primary Deuterium Isotope Effect with Solvent Composition for the Reaction of Di-(4-nitrophenyl)methane with t-Butoxide in t- Butyl Alcohol–Toluene Mixtures

Kinetics of Proton Transfer Reactions of Carbon Acids. V. Variation of Primary Deuterium Isotope Effect with Solvent Composition for the Reaction of Di-(4-nitrophenyl)methane with t-Butoxide in t- Butyl Alcohol–Toluene Mixtures

Proton-Transfer Reactions between Nitroalkanes and Hydroxide Ion under Non-Steady-State Conditions. Apparent and Real Kinetic Isotope Effects

Proton Transfer Reactions of Methylanthracene Radical Cations with Pyridine Bases under Non-Steady-State Conditions. Real Kinetic Isotope Effect Evidence for Extensive Tunneling

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