Slow proton transfer in the nitration of anthracene; determination of the kinetic isotope effect of hydrogen in the nitration of naphthalene and anthracene with nitronium tetrafluoroborate

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.

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Dimerization of 1,2-cyclohexadiene, a model for nonconcerted allene dimerization. Determination of a secondary deuterium kinetic isotope effect by deuterium nuclear magnetic resonance

Journal of the American Chemical Society ◽

10.1021/ja00768a066 ◽

1972 ◽

Vol 94 (13) ◽

pp. 4753-4754 ◽

Cited By ~ 16

Author(s):

William R. Moore ◽

Paul D. Mogolesko ◽

Daniel D. Traficante

Keyword(s):

Nuclear Magnetic Resonance ◽

Magnetic Resonance ◽

Isotope Effect ◽

Kinetic Isotope Effect ◽

Kinetic Isotope ◽

Nuclear Magnetic

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Ketonization equilibria of phenol in aqueous solution

Canadian Journal of Chemistry ◽

10.1139/v99-048 ◽

1999 ◽

Vol 77 (5-6) ◽

pp. 605-613 ◽

Cited By ~ 30

Author(s):

Marco Capponi ◽

Ivo G Gut ◽

Bruno Hellrung ◽

Gaby Persy ◽

Jakob Wirz

Keyword(s):

Aqueous Solution ◽

Proton Transfer ◽

Isotope Effect ◽

Kinetic Isotope Effect ◽

Flash Photolysis ◽

Equilibrium Constants ◽

Thermodynamic Cycle ◽

Acidity Constant ◽

Kinetic Isotope ◽

Carbon Acids

The two keto tautomers of phenol (1), cyclohexa-2,4-dienone (2) and cyclohexa-2,5-dienone (3), were generated by flash photolysis of appropriate precursors in aqueous solution, and the pH-rate profiles of their enolization reactions, 2 –> 1 and 3 –> 1, were measured. The rates of the reverse reactions, 1 –> 2 and 1 –> 3, were determined from the rates of acid-catalyzed hydron exchange at the ortho- and para-positions of 1; the magnitude of the kinetic isotope effect was assessed by comparing the rates of hydrogenation of phenol-2t and -2d. The ratios of the enolization and ketonization rate constants provide the equilibrium constants of enolization, pKE(2, aq, 25°C) = -12.73 ± 0.12 and pKE(3, aq, 25°C) = -10.98 ± 0.15. Combination with the acidity constant of phenol also defines the acidity constants of 2 and 3 through a thermodynamic cycle. These ketones are remarkably strong carbon acids: pKa(2) = -2.89 ± 0.12 and pKa(3) = -1.14 ± 0.15. They disappear by proton transfer to the solvent with lifetimes, τ(2) = 260 μs and τ(3) = 13 ms, that are insensitive to pH in the range from 3-10.Key words: proton transfer, tautomers, flash photolysis, kinetic isotope effect, pH-rate profiles.

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