X, A, 1 Gibbs and Brill: Diethijlsuccinosncchiate 59 



The color of the yellow form of ethylsuccinosuccinate is due 

 not to an absorption band in the visible region of the spectrum, 

 but to a band which lies so close to the visible region, heading 

 at 1/A=2,660, that at the higher concentrations it broadens into 

 the visible. Since the persistence and breadth of this band prob- 

 ably depend upon the relative amounts of enol and keto forms 

 present and since the diacetyl derivative gives no band at all, 

 it is quite possible that the pure enol form will be colorless and 

 that the absorption band heading at 1/A=2,660 may be absent. 

 The equilibrium existing between the two forms in alcohol solu- 

 tion has so far precluded the photographing of the pure enol 

 form without first fixing the labile hydrogen atoms. The band 

 of the keto from is not due solely to the =C0 groups in the 

 para position but to the influence exerted upon them by the 

 neighboring carboxyl groups. Tetrahydroquinone and its diox- 

 ime are colorless ; 







II 



H2 — V y — -112 



II 







it seems probable, however, that these compounds will show 

 absorption bands near the visible region of the spectrum, due in 

 the case of the former to the mutual influence of the carbonyl 

 groups, in a manner similar to that found in diacetyl. The 

 neighboring carboxyl groups in ethylsuccinosuccinate may 

 merely shift this band slightly so that it falls nearer the visible 

 region. 



Baeyer and Noyes '* found that tetrahydroquinone reacts with 

 acetyl chloride and forms a white precipitate in ether solution 

 on the addition of sodium alcoholate and that it, therefore, may 

 exist in two forms, the enol and keto. 



Diethylsuccinosuccinate in addition to the enol and keto, may 

 have stereoisomeric modifications, the cis and the trans forms. 

 Since stereoisomerism is only possible when the carbon atoms 

 to which the carboxyl groups are attached are saturated, wand- 

 ering hydrogen atoms in the 1, 4 positions in the keto form 

 preclude the existence of cis and trans modifications. It seems 

 reasonable to assume that in the keto form this change takes 



"Ber. d. deutschen chem. Ges. (1889), 22, 2168. 



