Proton Transfer Reactions of Triazol-3-ylidenes: Kinetic Acidities and Carbon Acid pKa Values for Twenty Triazolium Salts in Aqueous Solution

Proton transfer in aqueous solutions of 3-hydroxypyridin (3HP) has been studied by temperature jump relaxation and ultrasound absorption techniques. Two chemical relaxations have been observed. In the range pK1<pH<pK2 the slower of the two processes corresponds to proton transfer between the N and O atoms. A mechanism is proposed which describes the pH and concentration dependence of the relaxation time measured. Proton transfer involves two types of processes which operate in parallel: I. pseudomonomolecular, by consecutive diffusion-controlled protonation and deprotonation steps, and 2. bimolecular by diffusion-controlled proton transfer between the neutral 3HP molecule and its corresponding cation or anion. There is no evidence for direct monomolecular proton transfer within the hydration shell of the molecule (k→ ~ k← < 2 × 1O3 sec-1).

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Kinetics of proton transfer reactions involving hydroxypyrene-trisulphonate in aqueous solution by nanosecond laser absorption spectroscopy

Chemical Physics Letters ◽

10.1016/0009-2614(75)80188-6 ◽

1975 ◽

Vol 34 (1) ◽

pp. 1-6 ◽

Cited By ~ 47

Author(s):

Th. Förster ◽

S. Völker

Keyword(s):

Aqueous Solution ◽

Proton Transfer ◽

Absorption Spectroscopy ◽

Transfer Reactions ◽

Nanosecond Laser ◽

Laser Absorption Spectroscopy ◽

Laser Absorption ◽

Proton Transfer Reactions ◽

Kinetics Of

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Normal acid/base behaviour in proton transfer reactions to alkoxy substituted carbenes: estimates for intrinsic barriers to reaction and pKa values

Canadian Journal of Chemistry ◽

10.1139/v99-087 ◽

1999 ◽

Vol 77 (7) ◽

pp. 1230-1240 ◽

Cited By ~ 11

Author(s):

John Paul Pezacki

Keyword(s):

Proton Transfer ◽

Key Words ◽

Marcus Theory ◽

Transfer Reactions ◽

Acid Base ◽

Pka Values ◽

Proton Transfer Reactions ◽

Normal Acid

Theoretical Eigen curves can be drawn through Brønsted data for dimethoxycarbene (1), phenyltrimethyl-siloxycarbene (3a), 4-methylphenyl(trimethylsiloxy)carbene (3b), 4-methoxyphenyl(trimethylsiloxy)carbene (3c), and β-naphthyl(trimethylsiloxy)carbene (3d). The Brønsted plots for these data are clearly curved with α values near 1 when proton transfer is thermodynamically unfavourable and α values near 0 when proton transfer is thermodynamically favourable, suggesting that these carbenes behave as "normal" Brønsted bases. Estimates of the intrinsic barriers (ΔG0‡) for proton transfer reactions and of the pKa values for the conjugate acids of the carbenes, extracted from these theoretical curves, have been made. The magnitudes of the intrinsic barriers (ΔG0‡) for these proton transfer reactions determined by Eigen and Marcus theories are all 1-5 kcal mol-1, suggesting that these reactions are intrinsically fast. Small intrinsic barriers also imply "normal" acid/base behaviour. Extrapolated pKa values are also the first estimates for the pKa values of the conjugate acids of carbenes 1 and 3a-3d. Key words: carbenes, proton transfer reactions, carbocations, Marcus theory, Brønsted plots.

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Kinetics of proton-transfer reactions in aqueous solution. IV. Broensted slope for internally hydrogen-bonded weak acids

Journal of the American Chemical Society ◽

10.1021/ja00747a002 ◽

1971 ◽

Vol 93 (18) ◽

pp. 4350-4354 ◽

Cited By ~ 22

Author(s):

John Stuehr ◽

Mary C. Rose

Keyword(s):

Aqueous Solution ◽

Proton Transfer ◽

Transfer Reactions ◽

Weak Acids ◽

Proton Transfer Reactions ◽

Kinetics Of ◽

Hydrogen Bonded

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Photophysics of Ochratoxin A in Aqueous Solution

Zeitschrift für Naturforschung B ◽

10.1515/znb-2008-1111 ◽

2008 ◽

Vol 63 (11) ◽

pp. 1321-1326 ◽

Cited By ~ 7

Author(s):

Dörte Steinbrück ◽

Claudia Rasch ◽

Michael U. Kumke

Keyword(s):

Aqueous Solution ◽

Proton Transfer ◽

Ochratoxin A ◽

Photophysical Properties ◽

Proton Transfer Reaction ◽

Transfer Reactions ◽

Back Reaction ◽

Experimental Conditions ◽

Fluorescence Measurements ◽

Proton Transfer Reactions

Abstract The photophysics of Ochratoxin A (OTA) in aqueous solution strongly depends on the pH. Due to its molecular structure OTA is prone to an excited state proton transfer reaction, which rules the photophysical properties. Based on results of absorption and fluorescence measurements the rate constants of the proton transfer reactions (forward and back reaction) were determined and subsequently, the pK*a value was calculated. Based on the results, optimized experimental conditions for the analysis can be determined e. solvent conditions (HPLC chromatography) or excitation and emission wavelength (fluorescence spectroscopy).

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