XI. A, 2 Brill: Diethylsuccinosuccinate, II 71 



pound was not stable and decomposed at once in the air. An 

 attempt was made to photograph diketohexamethylene in the 

 presence of two equivalents of sodium ethylate, but decompo- 

 sition took place with darkening of the solution, and the absorp- 

 tion curve obtained was not different from the curve obtained 

 from the solution of the compound alone. This result taken with 

 that obtained by the titration of the alcoholic solution with al- 

 coholic bromine solution is considered conclusive evidence that 

 diketohexamethylene exists in alcoholic solution only in the keto 

 form. 

 Two forms are possible for p-hydroxyquinone. 







M II _ 



H— ^'^— OH g^r ^1=0 



H0-\/ 



and 

 -H 









Keto-enol. Keto-keto. 



As the potassium salt can exist in only the keto-enol form, 

 chloranil in only the keto form, and dichlordiethoxyquinone in 

 only the keto-enol form and as the absorption curves of these com- 

 pounds are very similar, the evidence is fairly conclusive for 

 the existence of p-hydroxyquinone in the keto-enol form. 



SUMMARY 



1. The absorption curves have been studied of dihydroxyte- 

 rephthalate in alcohol, and in the presence of two molecules of 

 sodium alcoholate; of p-diamidoterephthalate in alcohol, and in 

 the presence of two molecules of hydrochloric acid; of dike- 

 tohexamethylene in alcohol; of chloranil in glacial acetic acid; 

 of p-hydroxyquinone in alcohol; of the potassium salt of the 

 latter in dilute alcohol ; and of dichlordiethoxyquinone in alcohol. 



2. The spectra of both diketohexamethylene and dihydrote- 

 rephthalate shows selective absorption, thus affording new evid- 

 ence of the correctness of the theory that the selective absorption 

 of organic compounds is intimately associated with the partial 

 valency equilibrium of the compound. 



