SOLID-STATE REACTIONS STUDIED BY C-13 ROTOR-SYNCHRONIZED MAGIC ANGLE SPINNING 2-DIMENSIONAL EXCHANGE NMR .1. SELF-DIFFUSION AND THE TAUTOMERIC HYDROGEN SHIFT IN TROPOLONE

Two-dimensional carbon-13 magic angle spinning exchange NMR experiments with rotor-synchronized mixing times have been carried out for solid tropolone at 40-degrees-C and at variable spinning frequencies. At low spinning rates, a complicated spectrum is obtained with cross peaks linking different sidebands of the same carbon atom (''auto'' cross peaks) as well as ones linking sidebands of chemically different atoms that are exchanged by a tautomeric hydrogen shift process (''hetero'' cross peaks). The results are interpreted in terms of a translational diffusion mechanism in which tropolone molecules undergo lattice jumps between different sites. To retain the crystal order, certain lattice jumps require that the molecules undergo a concomitant hydrogen shift and/or a pi-flip about an axis in the molecular plane. From the results, a self-diffusion constant of D is-approximately-equal-to 4 x 10(-21) m2 s-1 is estimated for solid tropolone at room temperature.