A reagent panel comprised of seven aryl beta-D-N-acetylneuraminides was synthesized and then used to probe the mechanisms of nonenzymatic hydrolysis. These reactions proceeded via four independent pathways: (1) acid-catalyzed hydrolysis of the neutral molecule; (2) acid-catalyzed hydrolysis of the anionic form, or its kinetic equivalent spontaneous hydrolysis of the neutral form; (3) spontaneous hydrolysis of the anionic form; and (4) a base-promoted pathway. The pH-independent spontaneous hydrolysis of 4-nitrophenyl alpha-D-N-acetylneuraminide (5) occurs at a rate that is over 100 times faster than that of the corresponding reaction of 4-nitrophenyl O-D-N-acetylneuraminide (4a). Spontaneous hydrolyses of four aryl beta-D-N-acetylneuraminides displayed a beta(lg) value of -1.24 +/-0.16 (pH = 8.1, T= 100 degrees C), and at a pH value of 1.0 (50 degrees C), all seven panel members gave a beta(lg) value of 0.14 +/- 0.08. The aqueous ethanolyses of 4a and 5 gave similar products and displayed sensitivity parameters (m) in a standard Winstein-Grunwald analysis of -0.04 +/- 0.01 and +0.23 +/- 0.02, respectively. These results, plus the activation parameters calculated for the spontaneous hydrolyses of the anionic forms of 5 (Delta H = 116 +/- 2 U mol(-1) and Delta S = 27 +/- 4 J mol(-1) K-1) and 4a (Delta H = 138 3 U mol(-1) and AS = 59 +/-8 J mol(-1) K-1), are inconsistent with anomeric carboxylate assistance occurring during the hydrolysis reactions, and the likely cause for the enhanced reactivity of 5 in comparison to that of 4a is an increase in ground-state steric strain.