Chemical Shifts in the Nuclear Magnetic Resonance Absorption for Oxygen-17 in Oxy Ions<sup>1</sup>

Jackson, J. A.; Taube, Henry

doi:10.1021/j100890a010

Cited by 23 publications

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“…In any case our calculations support the exchange mechanism suggested earlier. 29,31 This mechanism is also in agreement with the observation that the rate of exchange is accelerated in acid solution.36 This is to be expected in view both of the increase of the relative concentrations of HCr04and Cr2072-and of the acid catalysis observed for reaction I.2, 28,36 A more detailed investigation of the oxygen exchange has recently been carried out by Baldwin and Holyer37 where the contribution of both reaction I and of the reaction involving OHis taken into account.…”

Section: Discussionsupporting

confidence: 64%

Kinetics of the hydrolysis of the dichromate ion. III. Environmental effects on rate constants and activation energies

Perlmutter-Hayman¹,

Weissmann²

1967

J. Phys. Chem.

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Section: Discussionsupporting

confidence: 64%

Kinetics of the hydrolysis of the dichromate ion. III. Environmental effects on rate constants and activation energies

Perlmutter-Hayman¹,

Weissmann²

1967

J. Phys. Chem.

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“…The Cr 2 O 7 2- signals appear at 1115 ppm (terminal) and 335 ppm (bridging), intensity ratio 6:1, and the chemical shift and line width of the 1115 ppm signal was shown to be independent of pH (7.0−3.0) and Cr(VI) concentration (0.02−0.32 M). This means that chemical exchange broadening as suggested by Figgis and co-workers 8 (eq 6) and H + -catalyzed hydrolysis of Cr 2 O 7 2- as observed by Jackson and Taube are not important rate processes under these conditions. However the CrO 4 2- /HCrO 4 - absorption (820−860 ppm) does show a pH dependence moving to lower frequencies and broadening as the pH is decreased.…”

Section: Resultsmentioning

confidence: 71%

¹⁷O NMR Study of Chromium(VI) Ions in Water

et al. 1996

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A mathematical model for oxygen exchange out of labeled (e.g., 17O) Na2CrO4 into solvent H2O according to the dimerization reaction 2CrO4 2- + 2H+ ⇌ (1/K a(HCrO 4 − )) 2HCrO4 - ⇌ (α/β) Cr2O7 2- + H2O is described. Two rates of isotopic change are identified: (1) a rapid change intimately associated with the attainment of chemical equilibrium, but not identical with it (rate constants ν1 and ν2, respectively), in which the fractional label in monomeric HCrO4 - + CrO4 2- (p) decreases more rapidly than that in the dimer Cr2O7 2- (q), i.e. ṗ > q̇, followed by (2) a slower decrease in both (q̇ > ṗ) until isotopic equilibrium with the solvent is established, p = q = r (rate constant ν3). Visible−UV and 17O NMR spectra have been used to characterize the elusive HCrO4 - ion. Vibrational fine structure is seen in the visible spectrum (C 3 v symmetry), and integration of the monomeric (HCrO4 - + CrO4 2-) 17O absorption agrees with only four O atoms in HCrO4 -. A pH-dependent shift to higher frequency (δCrO 4 2− = 812 ppm; δHCrO 4 − = 860 ppm) is used to give pK a(HCrO 4 − ) = 5.80 (I = 1.0 M, 25 °C), and comparisons with the integrated Cr2O7 2- signal (δCr 2 O 7 2− = 1115 ppm) give K d's for dimerization (= α/β) of 81 M-1 (I = 1.0 M) and 132 M-1 (I = 6.0 M), at 25 °C. Dimerization and hydrolytic rate constants (α and β) have been obtained under the conditions of the 17O exchange experiments; they are shown to contain spontaneous, buffer, and [H+] and [OH-] contributions in agreement with earlier investigations. 17O exchange out of enriched Na2CrO4 has been followed in aqueous solutions over the concentration range 0.01−2.0 M and over the pH range 6.38−13.0 at 25 °C and constant ionic strength (I = 1.0, 6.0). The dimerization reaction (eq 1) contributes only at the highest Cr(VI) concentration (2.0 M), and then only slightly (i.e., ∼10% at pH 7.3). The rate data have been interpreted in terms of the direct exchange paths Cr17O4 2- + H2O → (k 1) Cr17O3O2- + H2 17O; HCr17O4 - + H2O → (k 2) HCr17O3O- + H2 17O; H2Cr17O4 + H2O → (k 3) H2Cr17O3O + H2 17O; Cr2 17O7 2- + H2O → (k 4) Cr2 17O6O2- + H2 17O, with rate constants k 1 = 7.2 × 10-8 M-1 s-1, k 2 = 7.6 × 10-4 M-1 s-1, k 3 = 1.7 × 105 M-1 s-1 (I = 1.0 M, 25 °C), and k 4 = 4.1 × 10-3 M-1 s-1 (I = 6.0 M, 25 °C). The monomeric paths (but not the rate constants) agree with those found in an earlier study, but that involving Cr2O7 2- is new. Rate constants for 17O exchange are compared with those of other substitution reactions of HCrO4 - and Cr2O7 2-.

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“…20,21 In 1965, 17 O NMR was applied to the Cr 2 O 7 2À anion. 22,23 Soon aer, the 17 O NMR spectra of a range of other oxometalates were obtained. [24][25][26] In a systematic study of 17 O NMR parameters of POM structures, Klemperer and co-workers clearly established the relationship between chemical shi and metal-oxygen bond lengths.…”

Section: Introductionmentioning

confidence: 99%

17O NMR chemical shifts in oxometalates: from the simplest monometallic species to mixed-metal polyoxometalates

et al. 2014

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Chemical Shifts in the Nuclear Magnetic Resonance Absorption for Oxygen-17 in Oxy Ions¹

Cited by 23 publications

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Kinetics of the hydrolysis of the dichromate ion. III. Environmental effects on rate constants and activation energies

Kinetics of the hydrolysis of the dichromate ion. III. Environmental effects on rate constants and activation energies

¹⁷O NMR Study of Chromium(VI) Ions in Water

17O NMR chemical shifts in oxometalates: from the simplest monometallic species to mixed-metal polyoxometalates

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Chemical Shifts in the Nuclear Magnetic Resonance Absorption for Oxygen-17 in Oxy Ions1

Cited by 23 publications

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Kinetics of the hydrolysis of the dichromate ion. III. Environmental effects on rate constants and activation energies

Kinetics of the hydrolysis of the dichromate ion. III. Environmental effects on rate constants and activation energies

17O NMR Study of Chromium(VI) Ions in Water

17O NMR chemical shifts in oxometalates: from the simplest monometallic species to mixed-metal polyoxometalates

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Chemical Shifts in the Nuclear Magnetic Resonance Absorption for Oxygen-17 in Oxy Ions¹

¹⁷O NMR Study of Chromium(VI) Ions in Water