174 The Philippine Journal of Science wis 



shows only general absorption, while its red potassium salt gives 

 a broad absorption band heading at -= 3050. 



A 



In this case there is no possibility for quinoid formation in a 

 ring in connection with conjugated linking between unsaturated 

 groups, and the colored salts do not give absorption spectra 

 showing a band in the quinone region. There is, however, a 

 marked difference between the spectra of the salts and free 

 acid. Hantzsch represents the equilibrium of the former by the 

 formula : 



,N0 2 1 



H 3 C— C 



M 



This explains the change in optical properties that takes place 

 when the acid is converted into its salts, and corresponds to our 

 oxime structure. 



Certain diketones represented by the type of indandions are 

 colorless or very faintly yellow, but dissolve in alkaline solutions 

 giving highly colored salts. In this case the salt formation has 

 been shown to take place with a tautomeric change from the 

 keto to the enol form as represented by the formulas : 



/C=0 /C=0 



\ \ 



CeEU y>CHR — -> C6H4 aCR 



\>=0 \c— OH(M) 



Keto indandion. Enol indandion. 



The alkali salt exists in the conjugated form according to 

 Hantzsch 18 who represents this condition as 



O 



C 6 H 4 ^CR M 



\c— 0/ 



Conjugated enol salt of indandion. 



This class of compounds is evidently more nearly related to 

 the phthaloximes than are the nitrolic acids. There are several 

 important points of difference, however, that serve to throw light 



18 Ann. d. Chem. (Liebig) (1912), 392, 286. 



