CARBOCYCLIC COMPOUNDS. 



In addition to the series of aliphatic compounds, series of carbon 

 compounds are known in which the atoms of carbon three to nine 

 are linked together in a ring. Amongst them we find saturated and 

 unsaturated compounds. They do not form such a large group as the 

 aliphatic compounds except those which contain six atoms of carbon. 

 These form a special group by themselves known as the aromatic 

 and hydroaromatic compounds. 



Only a few, excluding the aromatic compounds, are found in 

 nature, the majority being synthetical products. They are termed 

 polymethylenes or cyclo-paraffins, cyclo-olefines and cyclo-diolefines. 

 Thus in the case of the hydrocarbons, we have : 



CH 



Trimethylene 

 or cyclopropane. 



f 1 T-I 1^ TT 



/ ^v^n VyjUfl 



CH 2 -CH 2 

 Tetramethylene 

 or cyclobutane. 



CH 2 CH 



CH 2 CH 



1 

 CH 2 CH 



Cyclobutene. 



,CH=rCH 



CH 2 



Cyclopentadiene. 

 CH 2 



CH 2 



X CH 2 CH 2 CH a 

 Heptamethylene 

 or cycloheptane 

 (suberane). 



CH 2 CH 3 

 CH 2 CH 2 



Hexamethylene 

 or hexahydrobenzene. 



Some of these hydrocarbons, chiefly alkyl derivatives of penta- 

 methylene and hexamethylene, are present in Galician and Russian 

 petroleum, and are known as naphthenes. They resemble the paraffins 

 in their properties. 



If hydrogen atoms be substituted by hydroxyl groups, ketonic 

 groups, carboxylic groups, such as in : 



CH 2 CH 2 CH 2 



CO 



CH 2 CH 2 CH 2 



Suberone, 



a series of compounds is formed which have the properties of aliphatic; 

 compounds into which they can be easily transforrnec). 



