ON HYDRO-AROMATIC COMPOUNDS WITH SINGLE NUCLEUS. 



131 



of the double bonds, theoretically possible in two isomeric forms, one 

 of which can exist in two stereoisomeric modifications. 



COOH 

 H,. Z'^, H 



H. .COOH 



H 



/\ 



Hv .COOH 



H 



hX, 



H, 

 COOH 



H„ 



X 



H 



H 



H, 



/\ 



H 



H„ 



H 



COOH H 



Cis trans A.,. 



H-^^^COOH 



Cis A,. 



DihydroterephthaVic acid, CfjHrXCOOH),. — Four possibilities depend- 

 ing on the position of the double bonds : one possibility appears in two 

 stereoisomeric modifications. 



H. yCOOH 



H 

 H 



/\ 



H 



/\ 

 COOH H 



Cis trans A.. ; 



H 



COOH 



H.. 



/^ 



H 



COOH 



As regards the resemblance to aliphatic compounds, the hexahydro-acids 

 do not give addition compounds with bromine, but substitution products 

 in which the bromine, as in the fatty series, occupies the a-position. The 

 tetrahydro-acids take up H, : Br., or HBr, forming hexahydro-compounds, 

 and the dihydro-acids combine with H, : Br2 or HBr, forming tetrahydro- 

 derivatives or with 2H2 : 2Br2 or 2 HBr, forming hexahydro-derivatives ;' 

 just as fatty compounds with two double bonds yield successively ethylene 

 derivatives and saturated fatty substances. When a tetrahydro-acid 

 absorbs hydrogen bromide the bromine atom occupies the position more 

 remote from the carboxyl group, resembling, for example, the production' 

 of /3-bromopropionic acid from acrylic acid and hydrogen bromide. The 

 bromo-acids on treatment with nascent hydrogen have the bromine 

 replaced by hydrogen, or if they contain two bromine atoms united to 

 adjacent carbon atoms then both bromine atoms are removed (i.) by 

 nascent hydrogen with formation of a double bond, or (ii.) by alcoholic 

 potash with formation of two double bonds. 



COOH cooa- • 



COOH COOH I I , •, ;•. 



CH C . CH C .. ^._ 



/X PHRr HP/'^CH H^^CHBr h/'^CH 



H,C 

 F..C 



CHBr 

 CHBr 



CH 

 COOH 



H.,C 



CH 



C 

 COOH 



2 : 3-Dibromohexahydro- 

 tereplithalic acid. 



A, : ;, Diliydrotere- 

 phtlialic acid. 



H. .CHBr 



CH 



I 

 COOH 



jS'y-Dibromadipic 

 acid. 



H^^CH 



C 



I 

 COOH 



Muconic acid. 



