The title aldehydes 1 and 3 exist in equilibrium with cyclic hemiacetal forms 2 and 4, respectively, with equilibrium constants in water of 6.7 (1 -2) and 20 (3 -4). These equilibria are displaced toward the hemiacetals in strongly basic solutions because of their ionization. Acidity constants have been determined to be 12.29 (2) and 12.38 (4). The kinetics of the equilibration have been studied in the pH range 1-8 in carboxylic acid and alkylphosphonic acid buffers. The base forms (RCOO" and RP031 2') produce a common Bronsted line, while the acid forms produce
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