Nuclear Magnetic Resonance Studies of the 1,4-Cyclohexanedione−Bromate−Acid Oscillatory System

The 1,4-cyclohexanedione-bromate-acid oscillating system was investigated using nuclear magnetic resonance (NMR) techniques. A range of NMR experiments were used which imaged pattern formation during the oscillations, probed the organic chemistry, and observed the presence of convection. Measurements of the change in concentration of key organic species, 1,4-cyclohexanedione, 2-bromo-1,4-cyclohexanedione, and 1,4-benzoquinone, with concurrent imaging of patterns, allowed partial validation of proposed reaction mechanisms. An investigation of the presence of convection, arising through density differences produced by the reaction, was made. It was found that convection was present in reaction solutions contained within 10 mm NMR tubes, but not 5 mm tubes. Pulsed gradient spin−echo (PGSE) experiments measuring the displacement of the solvent molecules found the dispersion (mobility) coefficients for the solvent increased, on average, by a factor of 3, from 1.3 × 10 -9 m 2 s -1 to 3.9 × 10 -9 m 2 s -1 (±0.02 × 10 -9 m 2 s -1 ), in the vertical direction where convection was present.