High-field NMR spectroelectrochemistry of spinning solutions: simultaneous in situ detection of electrogenerated species in a standard probe under potentiostatic control

Abstract

This report summarizes the design and performance of the first practicable in situ electrogenerative high-field solution-NMR cell, designed for simultaneous NMR spectroelectrochemistry in a conventional 10- or 16-mm 300 MHz probe. The axially symmetric three-electrode assembly is stationary and self-aligning. It dips into a standard spinning 10-mm sample tube and is adapted for convenient operation in any commercial high-field, multi-nuclear, variable-temperature FT NMR spectrometer. The tubular, rf-transparent working electrode (presently consisting of a gold film, coated on glass) completely spans the detection region; the recommended coating thickness is ≤0.01 δ, where δ is the rf-absorbing conductor skin depth. With careful shimming, very narrow 1H signals (∼1 Hz) can be obtained. The performance of the in situ NMR-electrochemical cell is illustrated by monitoring the progressive reduction of ‘ p-quinone’ (1,4-benzoquinone) to its dihydro-form by controlled-potential electrolysis in an acidic medium.