150 PROCEEDINGS OF THE AMERICAN ACADEMY 



V. On the Constitution of the Substituted Acrylic and 

 Propionic Acids. 



By Henry B. Hill. 



Within a few years the number of substituted acrylic and pro- 

 pionic acids known has been largely increased, and yet the constitution 

 of but few of these can be said to be satisfactorily established. In a 

 previous communication I was led to adopt provisionally for muco- 

 bromic acid the formula, — 



CBr^ — CHO 

 I 

 = C — COOH 



which explained its connection with maleic acid, in whose molecule the 

 researches of Fittig had shown the provable existence of a dyad 

 carbon atom. The structure of the related dibromacrylic acid was 

 then naturally expressed by the formula, — 



CBr^H 

 I 



c = 



I 

 COOH 



against which at the time nothing more convincing than a belief in its 

 improbability could be urged. The relations which Andrews and I 

 have shown to exist between this same acid and two different tribrom- 

 propionic acids prove, however, that this formula is incorrect. An acid 

 with this structure could be formed from but a single tribrompropionic 

 acid, and must of necessity give this same tribrompropionic acid by the 

 addition of hydrobromic acid. The same objection also applies with 

 equal force to the other two conceivable formulae for dibromacrylic 

 acid which contain dyad carbon, — 



= CH = CBr 



I I 



CBr^ and CHBr 



1 I 



COOH COOH 



