| Popis: |
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. Bronsted and Hammett type relationships are examined for this family of closely related substrates. The Bronsted 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. |
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