The line shape of the NMR signals of protons bonded to nitrogen shows that the longitudinal relaxation of N-14 (T-1N) is much faster for di-tert-butylpyridinium ions (DTBPH+) than for pyridinium (PyH+) in solution. The relaxation times for ring carbons (T-1C) indicate that the difference comes from a different rate of tumbling in solution, rather than from a difference in the electric field gradient. Computer modeling gives ratios of relaxation times (T-1N = 1/R-1N) Of 10-20, Ion pairing has an opposite effect upon the two ions: it accelerates the relaxation of PyH+ but slows down the relaxation of DTBPH+. In the absence of electrostatic interactions with the solvent, ion pairing should increase the correlation time tau(c) (decrease T-1) for the anion positioned in the plane of the ring and should have only a small effect on tau(c) for the anion perpendicular to the ring (along the z axis). The anion in the ion pair of PyH+ is positioned on the x axis (the C-2 axis of the ring) for maximum hydrogen bonding with the N-H group. The inability of DTBP to form hydrogen bonds at nitrogen was confirmed by the equality of its N-15 chemical shifts in methyl tert-butyl ether, dry and containing water. B3LYP/6-31C* calculations indicate that the positioning of an anion along the z axis of DTBPH+ induces a charge redistribution that reduces the electrostatic interaction of the cation with the solvent dipoles in the xy plane, thus decreasing the tumbling correlation time, tau(c), and increasing the NMR relaxation time, T-i. These data suggest that chemisorption of pyridine on acid sites on solid surfaces occurs with the nitrogen facing the surface but that DTBP is chemisorbed on the side (flatwise) with its degree of hydronation depending on the degree of curvature of the surface around the site.