Kinetic isotope effects and tunnelling in the proton-transfer reaction between 4-nitrophenylnitromethane and tetramethylguanidine in various aprotic solvents

1975 ◽  
Vol 71 (0) ◽  
pp. 1876 ◽  
Author(s):  
Edward F. Caldin ◽  
Salvador Mateo
Keyword(s):  
Proton Transfer ◽  
Transfer Reaction ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Proton Transfer Reaction ◽  
Aprotic Solvents ◽  
Kinetic Isotope

Kinetic study of the proton transfer reaction between 1-nitro-1-(4-nitrophenyl)alkanes and TBD and MTBD bases in acetonitrile solvent

2001 ◽  
Vol 79 (7) ◽  
pp. 1128-1134 ◽  
Author(s):  
Iwona Grzeskowiak ◽  
Wtodzimierz Galezowski ◽  
Arnold Jarczewski
Keyword(s):  
Proton Transfer ◽  
Kinetic Study ◽  
Transfer Reaction ◽  
Isotope Effects ◽  
Ion Pairs ◽  
Kinetic Isotope Effects ◽  
Proton Transfer Reaction ◽  
Comparable Amount ◽  
Kinetic Isotope ◽  
Proton Transfer Reactions

The rates of proton transfer reactions between C-acids of the series of nitroalkanes with increasing bulk of R = H, Me, Et, i-Pr substituent as: 4-nitrophenylnitromethane (0), 1-(4-nitrophenyl)-1-nitroethane (1), 1-(4-nitrophenyl)-1-nitropropane (2), 2-methyl-1-(4-nitrophenyl)-1-nitropropane (3) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) have been measured in acetonitrile at pseudo-first-order conditions. The product of the proton transfer reaction with MTBD in acetonitrile is dissociated into free ions while that of the TBD reaction is composed of a comparable amount of ions and ion pairs. The second-order rate constants (k2H) for these bases of almost equal strength in acetonitrile (pKa = 24.70, 24.97 for MTBD and TBD) and C-acids 1, 2, and 3 are: 317, 86, 7.6 dm3 mol–1 s–1; and 15 200, 5300, 1100 dm3 mol–1 s–1, respectively. The appropriate primary deuterium kinetic isotope effects (kH/kD) are 12.5, 10.8, 6.9; and 9.9, 11.2, 12.6. The influence of steric hindrance brought by reacting C-acids and bases is discussed. The different structure of the transition states and the products as mono- and double-hydrogen bonded complexes for these series of C-acids and MTBD and TBD bases is manifested by a distinct reaction mechanism which we attempt to explain.Key words: proton transfer, kinetic study, C-acids, organic bases, acetonitrile, kinetic isotope effects.

The proton transfer reaction between bis(2,4-dinitrophenyl)methane and nitrogen bases in dimethyl sulfoxide and toluene solvents

1991 ◽  
Vol 69 (3) ◽  
pp. 468-473 ◽  
Author(s):  
Arnold Jarczewski ◽  
Grzegorz Schroeder ◽  
Kenneth T. Leffek
Keyword(s):  
Proton Transfer ◽  
Dimethyl Sulfoxide ◽  
Isotope Effects ◽  
Equilibrium Constants ◽  
Activation Parameters ◽  
Kinetic Isotope Effects ◽  
Proton Transfer Reaction ◽  
Kinetic Isotope ◽  
Deuteron Transfer ◽  
Classical Region

Rate constants have been measured for the proton and deuteron transfer reactions of bis(2,4-dinitrophenyl)methane (1) with 1,1,3,3-tetramethylguanidine (TMG) and 1,5-diazabicyclo[5.4.0]undec-7-ene (DBU) in dimethyl sulfoxide (DMSO) and toluene solvents. Equilibrium constants, primary deuterium kinetic isotope effects, and activation parameters are reported. The reaction of 1 with DBU is faster than that with TMG by factors of 5 and 50 in toluene and DMSO respectively. The primary deuterium kinetic isotope effects, kH/kD = 7–9, which are independent of the polarity of the solvent, indicate an uncoupled mechanism of proton transfer and are in the "classical" region with little or no indication of a tunnelling contribution to the enthalpy of activation for these reactions. Key words: proton transfer, bis(2,4-dinitrophenyl)methane, deuterium isotope effects.

Phenyltetramethylguanidines: substituent effect on rates and isotope effects in their reaction with bis(4-nitrophenyl)cyanomethane in acetonitrile

1991 ◽  
Vol 69 (2) ◽  
pp. 205-210 ◽  
Author(s):  
Przemyslaw Pruszynski ◽  
Kenneth T. Leffek
Keyword(s):  
Proton Transfer ◽  
Transfer Reaction ◽  
Isotope Effects ◽  
Proton Transfer Reaction ◽  
Kinetic Isotope ◽  
Reaction Constant ◽  
Base Strength ◽  
Derivatives Of ◽  
Best Fit ◽  
Hammett Relationship

A series of 22 phenyl substituted derivatives of 2-phenyl-1,1′,3,3′-tetramethylguanidine were used as bases in the proton transfer reaction from bis(4-nitrophenyl)cyanomethane in acetonitrile solvent. Brønsted and Hammett type relationships are examined for this family of closely related substrates. The Brønsted relationship constructed from the pKa values determined in acetonitrile shows β = 0.55 ± 0.03. The best fit of the Hammett relationship, with special values for p-NO2 and p-CN groups, gives the reaction constant ρ = −1.39 ± 0.1. The kinetic isotope effect, kH/kD, increases from 9.6 to 12.4 at 25 °C with decreasing base strength, i.e., when the reaction becomes more thermoneutral. Key words: tetramethylguanidine, proton transfer, deuterium isotope effects.

Kinetics and isotope effects of the proton transfer reactions between 1-(4-nitrophenyl)-1-nitroethane to phenyltetramethylguanidine in dipolar aprotic solvents

1984 ◽  
Vol 62 (5) ◽  
pp. 954-957 ◽  
Author(s):  
Arnold Jarczewski ◽  
Przemyslaw Pruszynski ◽  
Mohammed Kazi ◽  
Kenneth T. Leffek
Keyword(s):  
Proton Transfer ◽  
Transfer Reaction ◽  
Isotope Effects ◽  
Proton Transfer Reaction ◽  
Transfer Reactions ◽  
Aprotic Solvents ◽  
Enthalpy Of Activation ◽  
Proton Transfer Reactions ◽  
Carbon Acid ◽  
Dipolar Aprotic Solvents

The carbon acid 1-(4-nitrophenyl)-1-nitroethane reacts with phenyltetramethylguanidine in the aprotic solvents acetonitrile, benzonitrile, and chlorobenzene in a bimolecular proton transfer reaction. The primary isotope effects, kH/kD, for these reactions at 25 °C are 8.5 ± 0.4, 6.1 ± 0.4, and 16 in acetonitrile, benzonitrile, and chlorobenzene respectively. The magnitude of the isotope effects on the enthalpy of activation [Formula: see text] are 2.3 ± 0.2, 1.6 ± 0.7, and 4.2 ± 0.6 kcal mol−1, which indicates a contribution from proton tunnelling to the reaction rate of the normal substrate.

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