The first of these possibilities is probed experimentally with comparison to solid powders of O NMR models compared to experimental spectra of KHCO 3 (s) (23.5 T, 20 kHz MAS, 33.0 h, hahnecho). To the side, illustrations of the crystal structure of KHCO 3 (s) show the unique oxygen (red) environments, as well as samples of the hydrogen (white) positions in the dynamic case (grey = carbon, purple = potassium). (C) A plot of O isotropic shift of all the now equivalent (under exchange) dynamic oxygen environments against the projection (onto the oxygenoxygen axis) of oxygen-proton distance of all the MD samples, the mean δ iso is marked (further illustrations of the same data are shown in Figs. ).