126 MOLECULAR STRUCTURE 



chemistry, e. g. the active bromosuccinic esters gradually 

 lose their power of rotation, by becoming converted into 

 a mixture or compound of the optical antipodes 1 . This 

 phenomenon is one especially noticed in halogen, and chiefly 

 in bromine compounds, and probably explains why reactions 

 carried out on such compounds have often given quite 

 unexpected results ; one of the most remarkable instances 

 is that active bromosuccinic acid gives one malic acid with 

 alkalies, but with silver oxide the optical antipode 2 . At 

 present, therefore, these halogen compounds should, as far 

 as possible, be excluded from determinations of constitution 

 in this province. 



3. TAUTOMEKJSM. 



The phenomenon of tautomerism is that a compound 

 shows an apparently different constitution according to the 

 reagent that acts on it. This has been observed, e. g., in 

 aceto-acetic ether, C 2 H 3 OCH 2 C0 2 C 2 H 5 , and led to two 

 constitutional formulae, one proposed by Frankland, 



H 3 CCOCH 2 C0 2 C 2 H 5 , 

 and the other supported by Geuther, 



H 3 CC(OH) = CHC0 2 C 2 H 5 . 



The first formula is based, inter alia, on the fact that 

 with potash a decomposition takes place with formation of 



acetone, 



H 3 CCOCH 3 . 



The second is in accord with the formation inter alia of the 

 body : 



H 3 CC = CHC0 2 C 2 H 5 



N(C 2 H 5 ) 2 , 



by the action of diethylamine, HN(C 2 H 5 ) 2 . 



The explanation of this peculiar behaviour was sought 



1 Walden, Berl. Ber. 31. 1416. 2 1. c. 



