pH-Free Measurement of Relative Acidities, Including Isotope Effects

Perrin, Charles L.

doi:10.1016/bs.mie.2017.07.012

Cited by 3 publications

(2 citation statements)

References 73 publications

(22 reference statements)

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“…It may be noted that linear least-squares analysis of one of those NMR titrations gave a correlation coefficient of 0.999999. A detailed guide to the method has been published [67].…”

Section: Nmr Titration a Brief Digressionmentioning

confidence: 99%

Symmetry of Hydrogen Bonds: Application of NMR Method of Isotopic Perturbation and Relevance of Solvatomers

Perrin

2023

Molecules

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Short, strong, symmetric, low-barrier hydrogen bonds (H-bonds) are thought to be of special significance. We have been searching for symmetric H-bonds by using the NMR technique of isotopic perturbation. Various dicarboxylate monoanions, aldehyde enols, diamines, enamines, acid–base complexes, and two sterically encumbered enols have been investigated. Among all of these, we have found only one example of a symmetric H-bond, in nitromalonamide enol, and all of the others are equilibrating mixtures of tautomers. The nearly universal lack of symmetry is attributed to the presence of these H-bonded species as a mixture of solvatomers, meaning isomers (or stereoisomers or tautomers) that differ in their solvation environment. The disorder of solvation renders the two donor atoms instantaneously inequivalent, whereupon the hydrogen attaches to the less well solvated donor. We therefore conclude that there is no special significance to short, strong, symmetric, low-barrier H-bonds. Moreover, they have no heightened stability or else they would have been more prevalent.

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“…It may be noted that linear least-squares analysis of one of those NMR titrations gave a correlation coefficient of 0.999999. A detailed guide to the method has been published [67].…”

Section: Nmr Titration a Brief Digressionmentioning

confidence: 99%

Symmetry of Hydrogen Bonds: Application of NMR Method of Isotopic Perturbation and Relevance of Solvatomers

Perrin

2023

Molecules

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“…As proof of concept, we determine the p K a of a range of acids and bases in 50% (v/v) 1-propanol/water, 50% (v/v) dimethyl sulfoxide- d 6 (DMSO)/water, and 30% (v/v) acetonitrile- d 3 (CD 3 CN)/water at 298 K. The uncertainties in the fitted p K a values are less than 0.5 units in most cases, while agreement with literature data is obtained within these uncertainties. While NMR is an established tool to determine the relative p K a values of organic molecules, to the best of our knowledge, the direct measurement of absolute p K a by NMR has not previously been described. All processing can be performed using the automation routines provided in Section S10 of the Supporting Information and the spreadsheet accompanying this work.…”

Section: Introductionmentioning

confidence: 99%

Measurement of the pK_a Values of Organic Molecules in Aqueous–Organic Solvent Mixtures by ¹H NMR without External Calibrants

Wallace,

Abiama,

Chipembere

2023

Anal. Chem.

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Aqueous–organic solvent mixtures are commonly used for reactions or analyses, where the components of a system are insoluble in pure water. The acid dissociation constant is an important property to measure in these media as it determines the charge state, solubility, and reactivity of a molecule. While NMR spectroscopy is an established tool for the measurement of pK a in water, its use in aqueous–organic solvents is greatly hindered by the requirement for external calibrants on which a working pH scale is set. Such calibrants include buffer solutions, “anchor” molecules with known pK a values, and pH electrodes that have undergone lengthy calibration procedures in the solvent mixture of interest. However, such calibrations are often inconvenient to perform, while literature pK a data covering the required range may not be available at the solvent composition or the temperature of interest. Here, we present a method to determine pK a in aqueous–organic solvents directly by NMR. We first determine pK a of an organic acid such as 2,6-dihydroxybenzoic acid (2,6-DHB) by measuring its 1H chemical shift as a function of concentration along a concentration gradient using chemical shift imaging (CSI). Using 2,6-DHB as a reference, we then determine pK a of less acidic molecules in single CSI experiments via the variation of their 1H chemical shifts along pH gradients. As proof of concept, we determine the pK a values of organic acids and bases up to pK a 10 in 50% (v/v) 1-propanol/water, 50% (v/v) dimethyl sulfoxide/water, and 30% (v/v) acetonitrile/water and obtain good agreement with the literature values.

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Vibrational spectroscopic study of isotopic effect on TcX3+ and TcX3OH (X: O, S and Se) by DFT

Arı

Büyükmumcu

Özpozan

2018

Journal of Molecular Structure

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pH-Free Measurement of Relative Acidities, Including Isotope Effects

Cited by 3 publications

References 73 publications

Symmetry of Hydrogen Bonds: Application of NMR Method of Isotopic Perturbation and Relevance of Solvatomers

Symmetry of Hydrogen Bonds: Application of NMR Method of Isotopic Perturbation and Relevance of Solvatomers

Measurement of the pK_a Values of Organic Molecules in Aqueous–Organic Solvent Mixtures by ¹H NMR without External Calibrants

Vibrational spectroscopic study of isotopic effect on TcX3+ and TcX3OH (X: O, S and Se) by DFT

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pH-Free Measurement of Relative Acidities, Including Isotope Effects

Cited by 3 publications

References 73 publications

Symmetry of Hydrogen Bonds: Application of NMR Method of Isotopic Perturbation and Relevance of Solvatomers

Symmetry of Hydrogen Bonds: Application of NMR Method of Isotopic Perturbation and Relevance of Solvatomers

Measurement of the pKa Values of Organic Molecules in Aqueous–Organic Solvent Mixtures by 1H NMR without External Calibrants

Vibrational spectroscopic study of isotopic effect on TcX3+ and TcX3OH (X: O, S and Se) by DFT

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Measurement of the pK_a Values of Organic Molecules in Aqueous–Organic Solvent Mixtures by ¹H NMR without External Calibrants