ORGANIC MEDICINAL CHEMICALS 39 



CLASS II. BENZENE OR AROMATIC SERIES 



i. HYDROCARBONS of this series are compounds containing carbon and 

 hydrogen, having the carbon atoms connected in a ring thus, 

 CH 



benzene, C 6 H 6 , 



HC 



HC/ l N^ CH 



6 



CH 



CH 



2. HALOGEN SUBSTITUTION PRODUCTS have an atom of hydrogen replaced 

 by a halogen atom thus, mono-chlor-benzene, CeHsCl; dibrom- 

 benzene, C 6 H 4 Br 2 . C 6 H B is called the phenyl radical; C 6 H 4 , the 

 phenylene radical. 



The di-substitution products may form three isomers accord- 



CBr 



HCfNcBr 



ing as the two are adjacent in the ring thus, 



HCl JCH 



CH 



called ortho-di-brom-benzene; or as they have an atom of 



CBr 



HC X N CH 

 hydrogen between thus, , called meta-di-brom- 



HC 



CBr 



\X 

 CH 



benzene; or as the atoms are opposite thus. 



CH 



CBr 

 called para-di-brom-benzene. 



When three atoms are substituted, we have symmetrical 

 CBr CBr 



HC/^CBr 



BrC 



CBr 



tri-brom-benzene; asymmetrical 



tri- 



CH 



v /r -v / 



CH CBr CBr 



HCf'NcBr 



brom-benzene; and adjacent tri-brom-benzene. 



HC 



This method of nomenclature is used whenever any element 

 or group takes the place of hydrogen. 



3. SULPHUR DERIVATIVES of the aromatic series are analogous to those of 

 the fatty acid series thus, benzene sulphonic acid, C 6 H 5 SO 3 H. 



