Isotope Effects on Chemical Equilibria. Part I. Some Secondary Isotope Effects of the Second Kind

1973 ◽  
Vol 51 (3) ◽  
pp. 411-421 ◽  
Author(s):  
D. J. Barnes ◽  
J. M. W. Scott
Keyword(s):  
Acetic Acid ◽  
Dissociation Constants ◽  
Isotope Effects ◽  
Chemical Equilibria

Secondary isotope effects Ka(H)/Ka(D) for the isotopic acid pairs 4-X-C6H4CH2COOH/4-X-C6H4-CD2COOH(X = H, NO2, OMe) have been determined at T = 25 °C by conductance measurements. This has involved the redetermination of the dissociation constants for the non-deuterated acids and in the case of X = NO2, OCH3, the new Ka values are to be preferred. The Ka of acetic acid has also been redetermined as a check on the reliability of the new data. The three isotope effects are shown to be much smaller than might have been anticipated on the basis of the e.m.f. measurements on the pair PhCH2COOH/PhCD2COOH reported earlier (1).

Isotope Effects on Chemical Equilibria. Part II. Some Further Secondary Isotope Effects of the Second Kind

1974 ◽  
Vol 52 (10) ◽  
pp. 1966-1972 ◽  
Author(s):  
Douglas James Barnes ◽  
Peter David Golding ◽  
John Marshall William Scott
Keyword(s):  
Isotope Effect ◽  
Dissociation Constants ◽  
Isotope Effects ◽  
Equilibrium Constants ◽  
Chemical Equilibria

The ratio of the dissociation constants Ka(H)/Ka(D) has been measured conductimetrically for the isotopic pairs XCH2COOH/XCD2COOH where X = Cl, PhO, and PhS. Methods of calculating the ratio of the equilibrium constants are considered in some detail. Since the isotope effect varies with the nature of the X substituent it is concluded that the simple inductive description of these effects is not tenable.

scholarly journals NMR of Natural Products as Potential Drugs

Molecules ◽  
2021 ◽  
Vol 26 (12) ◽  
pp. 3763
Author(s):  
Poul Erik Hansen
Keyword(s):  
Natural Products ◽  
Hydrogen Bonding ◽  
Density Functional ◽  
Chemical Shifts ◽  
Isotope Effects ◽  
Density Functional Theory Calculations ◽  
Intramolecular Hydrogen Bonding ◽  
Chemical Equilibria ◽  
Nmr Techniques ◽  
Intramolecular Hydrogen

This review outlines methods to investigate the structure of natural products with emphasis on intramolecular hydrogen bonding, tautomerism and ionic structures using NMR techniques. The focus is on 1H chemical shifts, isotope effects on chemical shifts and diffusion ordered spectroscopy. In addition, density functional theory calculations are performed to support NMR results. The review demonstrates how hydrogen bonding may lead to specific structures and how chemical equilibria, as well as tautomeric equilibria and ionic structures, can be detected. All these features are important for biological activity and a prerequisite for correct docking experiments and future use as drugs.

α-DEUTERIUM KINETIC ISOTOPE EFFECTS IN SOLVOLYSES OF endo-NORBORNYL p-BROMOBENZENESULFONATE

1965 ◽  
Vol 43 (8) ◽  
pp. 2254-2258 ◽  
Author(s):  
C. C. Lee ◽  
Edward W. C. Wong
Keyword(s):  
Acetic Acid ◽  
Formic Acid ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Aqueous Dioxane ◽  
Kinetic Isotope ◽  
Different Temperatures

endo-Norbornyl-2-d p-bromobenzenesulfonate was synthesized and the isotope effects, as measured by kH/kD, were determined over a range of temperatures for solvolyses in 30% water – 70% dioxane, acetic acid, and formic acid. Values of kH/kD are of the order of 1.20. The data appear to indicate slightly higher isotope effects as the solvents are changed from aqueous dioxane to acetic acid to formic acid, as well as somewhat higher isotope effects at lower temperatures. Possible mechanistic implications of these results are presented. Relative titrimetric acetolysis rates, kexo/kendo, at different temperatures, and enthalpies and entropies of activation for these acetolyses are evaluated and discussed.

Carbon-13 Isotope Effects in the Oxidation of Acetic Acid

1965 ◽  
Vol 69 (4) ◽  
pp. 1428-1429 ◽  
Author(s):  
Mieczyslaw Zielinski
Keyword(s):  
Acetic Acid ◽  
Isotope Effects

Chemistry of episulfides. II. The reactivities of propylene sulfide and propylene oxide towards acetic acid

1968 ◽  
Vol 46 (7) ◽  
pp. 1043-1046 ◽  
Author(s):  
Neil S. Isaacs ◽  
K. Neelakantan
Keyword(s):  
Acetic Acid ◽  
Propylene Oxide ◽  
Isotope Effects ◽  
Preexponential Factor ◽  
Solvent Isotope ◽  
Solvent Isotope Effects

The rates and products of solvolysis of propylene oxide and propylene sulfide in acetic acid have been determined. The results show that terminal attack is preferred, although not exclusively, and that the sulfide is the less reactive by a factor of 50–60. This difference is accounted for mainly in the preexponential factor. Solvent isotope effects are also observed.

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