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- W1963729713 abstract "Rates and equilibirum constants have been determined for the proton-transfer reaction of 4-nitrophenylnitromethane, NO2C6H4CH2NO2, and its αα-deuterated analogue NO2C6H4CD2NO2, with the strong base tetramethylguanidine [HNC(NMe2)2], at temperatures between –60°C and + 65°C in a range of aprotic solvents. Spectrophotometry and the stopped-flow technique were used. The reaction is a simple proton-transfer process leading to an ion-pair. The kinetic isotope effects are correlated with the polarity of the solvents, as measured by the dielectric constant or by the empirical parameter ET. In the less polar solvents they are exceptionally large. In toluene, for example, at 25°C the rate ratio kH/kD= 45 ± 2, the activation energy difference EDa–EHa= 4.3 ± 0.3 kcal mol–1(16 kJ mol–1), and the ratio of the pre-exponential factors log10(AD/AH)= 1.5 ± 0.2; and even larger values of log10(AD/AH) are found for mesitylene (1.94 ± 0.06) and cyclohexene (2.4 ± 0.2). Positive deviations from linear Arrhenius plots are found for these solvents. Tunnelling is the only interpretation that can account for these results. For the more polar solvents (dielectric constant 7 to 37), the isotope effects are closer to the range predicted by semi-classical theory." @default.
- W1963729713 created "2016-06-24" @default.
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- W1963729713 date "1975-01-01" @default.
- W1963729713 modified "2023-09-26" @default.
- W1963729713 title "Kinetic isotope effects and tunnelling in the proton-transfer reaction between 4-nitrophenylnitromethane and tetramethylguanidine in various aprotic solvents" @default.
- W1963729713 doi "https://doi.org/10.1039/f19757101876" @default.
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