Kinetic isotope effect and tunnelling in the proton transfer reaction between 2,4,6-trinitrotoluene and 1,1′,3,3′-tetramethylguanidine in dimethylformamide solvent

1979 ◽  
Vol 57 (6) ◽  
pp. 669-672 ◽  
Author(s):  
Arnold Jarczewski ◽  
Przemyslaw Pruszynski ◽  
Kenneth T. Leffek
Keyword(s):  
Proton Transfer ◽  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Transfer Reaction ◽  
Proton Transfer Reaction ◽  
Deuterium Isotope Effect ◽  
Kinetic Isotope ◽  
Enthalpy Of Activation ◽  
Entropy Of Activation ◽  
Large Primary

The proton transfer reaction between 2,4,6-trinitrotoluene and 1,1′,3,3′-tetramethylguanidine in dimethylformamide solvent shows a large primary deuterium isotope effect, kH/kD = 24.3 at 0 °C and 16.9 at 20 °C. The enthalpy of activation difference (ΔHD≠ − ΔHH≠) = 2.6 ± 0.4 kcal mol−1 and the entropy of activation difference (ΔSD≠ − ΔSH≠) = 3.4 ± 1.3 cal mol−1 K−1. This isotope effect, when fitted to Bell's equation, indicates that there is a considerable contribution to this reaction from tunnelling of the proton through the potential energy barrier.

Kinetics and Stereochemistry of Elimination of Nitrous-Acid From 1-Para-Nitrophenyl-2-Nitroethyl Derivatives

1986 ◽  
Vol 39 (2) ◽  
pp. 281 ◽  
Author(s):  
RK Norris ◽  
TA Wright
Keyword(s):  
Isotope Effect ◽  
Nitrous Acid ◽  
Kinetic Isotope Effect ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Positive Entropy ◽  
Kinetic Isotope ◽  
Entropy Of Activation ◽  
Large Primary

The eliminations of nitrous acid from the compounds (1) and (6) are E2 processes, which proceed with a large primary kinetic isotope effect and with antiperiplanar stereochemistry. The rate of elimination of HNO2 from (1) is intermediate between the rate of elimination of HCl from (4) and HBr from (5). This order of nucleofugality , namely Br- > NO2- > Cl -, results from a more positive entropy of activation for the elimination of nitrous acid. The presence of an α-chlorine, as in compounds (8), (28) and (29), leads to elimination processes which are E1cB-like, with low primary kinetic isotope effects and with lack of stereospecificity.

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

1974 ◽  
Vol 52 (4) ◽  
pp. 592-596 ◽  
Author(s):  
Jae-Hang Kim ◽  
Kenneth T. Leffek
Keyword(s):  
Proton Transfer ◽  
Isotope Effect ◽  
Activation Parameters ◽  
Proton Transfer Reaction ◽  
Transfer Reactions ◽  
Deuterium Isotope Effect ◽  
Enthalpy Of Activation ◽  
Proton Transfer Reactions ◽  
Carbon Acids ◽  
Kinetics Of

The primary deuterium isotope effect has been measured for the proton transfer reaction from di-(4-nitrophenyl)methane to t-butoxide ion in a solvent consisting of 10% v/v toluene in t-butanol at a series of temperatures between 20 and 45 °C. The isotopic rate ratio, kH/kD, is 7.3 at 25 °C. The activation parameters showed an enthalpy of activation difference (ΔHD≠ − ΔHH≠) of only ca. [Formula: see text] kcal mol−1 and an entropy isotope effect (ΔSD≠ − ΔSH≠) of −2.4 cal mol−1 deg−1. The latter indicates, according to the theory of Bell, that tunnelling of the proton through the energy barrier is unimportant in this reaction. This result is compared to other reactions in the literature, in which tunnelling has been postulated to occur.

scholarly journals Pressure dependence of the deuterium isotope effect in the photolysis of formaldehyde by ultraviolet light

2010 ◽  
Vol 10 (7) ◽  
pp. 3455-3462 ◽  
Author(s):  
E. J. K. Nilsson ◽  
V. F. Andersen ◽  
H. Skov ◽  
M. S. Johnson
Keyword(s):  
Isotope Effect ◽  
Pressure Dependence ◽  
Kinetic Isotope Effect ◽  
Ambient Pressure ◽  
Deuterium Isotope Effect ◽  
Kinetic Isotope ◽  
Molecular Channel ◽  
The University ◽  
First Time ◽  
Gas Pressures

Abstract. The pressure dependence of the relative photolysis rate of HCHO vs. HCDO has been investigated for the first time, using a photochemical reactor at the University of Copenhagen. The dissociation of HCHO vs. HCDO using a UVA lamp was measured at total bath gas pressures of 50, 200, 400, 600 and 1030 mbar. The products of formaldehyde photodissociation are either H2 + CO (molecular channel) or HCO + H (radical channel), and a photolysis lamp was chosen to emit light at wavelengths that greatly favor the molecular channel. The isotope effect in the dissociation, kHCHO/kHCDO, was found to depend strongly on pressure, varying from 1.1 + 0.15/−0.1 at 50 mbar to 1.75±0.10 at 1030 mbar. The results can be corrected for radical channel contribution to yield the kinetic isotope effect for the molecular channel; i.e. the KIE in the production of molecular hydrogen. This is done and the results at 1030 mbar are discussed in relation to previous studies at ambient pressure. In the atmosphere the relative importance of the two product channels changes with altitude as a result of changes in pressure and actinic flux. The study demonstrates that the δD of photochemical hydrogen produced from formaldehyde will increase substantially as pressure decreases.

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