Elementary Steps in Acid-Base Catalysis. Proton Transfer Reactions in Aqueous Solutions

1968 ◽  
Vol 7 (10) ◽  
pp. 818-819 ◽  
Author(s):  
M.-L. Ahrens ◽  
G. Maass
Keyword(s):  
Proton Transfer ◽  
Aqueous Solutions ◽  
Base Catalysis ◽  
Transfer Reactions ◽  
Acid Base ◽  
Elementary Steps ◽  
Proton Transfer Reactions

Acid-Base Catalysis and Proton-Transfer Reactions

2007 ◽  
pp. 321-359
Author(s):  
Luis Arnaut ◽  
Sebastiao Formosinho ◽  
Hugh Burrows
Keyword(s):  
Proton Transfer ◽  
Base Catalysis ◽  
Transfer Reactions ◽  
Acid Base ◽  
Proton Transfer Reactions

Proton transfer reactions in aqueous solutions of pyridoxamine phosphate

1988 ◽  
Vol 16 (4) ◽  
Author(s):  
J. Reiter ◽  
P. Schuster ◽  
H. Winkler ◽  
F. Eggers
Keyword(s):  
Proton Transfer ◽  
Aqueous Solutions ◽  
Transfer Reactions ◽  
Proton Transfer Reactions

Protonenübertragungsreaktionen zweibasischer Säuren in wäßriger Lösung: 3-Hydroxypyridin / Proton Transfer Reactions of Dibasic Acids in Aqueous Solution: 3-Hydroxypyridine

1976 ◽  
Vol 31 (5-6) ◽  
pp. 219-224 ◽  
Author(s):  
P. Schuster ◽  
K. Tortschanoff ◽  
H. Winkler
Keyword(s):  
Aqueous Solution ◽  
Relaxation Time ◽  
Proton Transfer ◽  
Aqueous Solutions ◽  
Hydration Shell ◽  
Transfer Reactions ◽  
Diffusion Controlled ◽  
Ultrasound Absorption ◽  
Proton Transfer Reactions

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).

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

1999 ◽  
Vol 77 (7) ◽  
pp. 1230-1240 ◽  
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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