
%0 Journal Article
%A Korsch, BH 
%A Riggs, NV 
%T Structure and Acid Strength of Opianic Acid and Its N-Methyl Oxime
%J Australian Journal of Chemistry
%D 1963/08/01
%V 16
%N 4
%P 709-716
%K 
%R https://doi.org/10.1071/CH9630709
%U https://www.publish.csiro.au/paper/CH9630709 
%X In water, undissociated opianic acid exists as an equilibrium mixture containing c. 30% of lactol form (Ia) in equilibrium with open-chain form (IIa); the carboxyl group is therefore a stronger acid by c. 0.5 pK units than the measured value (pK 3.06 ± 0.03) indicates. Opianic acid N-methyl oxime exists largely as the classical nitrone carboxylic acid (IIIa) in water, and is slightly weaker (pK 2.6-2.7) than opianic acid. Both compounds exist largely as cyclic forms, (Ia) and (IV), respectively, in chloroform. 
