Knowledge Bank

“The chemical shifts of the 2-, 6-, and 8- protons in purine have been assigned by deuterium substitution. A pronounced concentration dependence of these proton chemical shifts is observed over the concentration rage of 0.05 to 1.0 molal. These data have been shown to be consistent with the osmotic studies of Ts’o et $al,1$ where the deviation of these solutions from ideality has been attributed to an association process proceeding beyond the dimmer stage with equal equilibrium constants for all successive steps. The chemical shift data also suggest vertical stacking of these molecules rather than a horizontal hydrogen-bonding type association. Substituent and solvent effects upon the above association will also be discussed.”