OXYGEN-17 NUCLEAR MAGNETIC RESONANCE STUDY OF THE CHROMATE REACTION WITH DICHROMATE

Abstract
The 17O n.m.r. spectra from aqueous solutions containing both chromate and dichromate ions have been obtained over a range of concentrations. Signals from both the bridging oxygen and the terminal oxygens in the dichromate ion have been observed. The line widths for the dissolved species were found to be concentration dependent. The variations in line width have been ascribed to a rapid reaction occurring at equilibrium between chromate and dichromate ions. The bimolecular rate constant for the reaction is 2.3 ± 0.4 × 103 1 mole−1 s−1 at 27 °C. The reaction mechanism is discussed in the general context of nucleophilic attack on dichromate ion. A comparison of this rate constant with those for the analogous reaction using different nucleophiles indicates that it is polarizability rather than basicity which determines nucleophilic reactivity towards Cr2O7.

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