Into two groups: (r) those exhibiting properties closely analogous to the aliphatic series - the polymethylenes, and (2) a series exhibiting properties differing in many respects from the aliphatic and polymethylene compounds, and characterized by a peculiar stability which is to be associated with the disposition of certain carbon valencies not saturated by hydrogen - the " aromatic series."
Polymethylenes can give only secondary and tertiary alcohols, benzene only tertiary; these latter compounds are known as phenols.
Two primary divisions of carbocyclic compounds may be conveniently made: (I) those in which the carbon atoms are completely saturated - these are known by the generic term polymethylenes, their general formula being (CH 2), t: it will be noticed that they are isomeric with ethylene and its homologues; they differ, however, from this series in not containing a double linkage, but have a ringed structure; and (2) those containing fewer hydrogen atoms than suffice to saturate the carbon valencies - these are known as the aromatic compounds proper, or as benzene compounds, from the predominant part which benzene plays in their constitution.
The presence of the heptamethylene ring in these compounds is shown by the production of suberone by the exhaustive methylation, &c., of hydroecgoni dine ethyl ester (see POLYMETHYLENES and TROPINE).
Many cyclic ketones are known, and in most respects they resemble the ordinary aliphatic ketones (see Polymethylenes; Terpenes).
POLYMETHYLENES, in chemistry, cyclic compounds, the simplest members of which are saturated hydrocarbons of general formula C 7, H 2nj where n may be r to 9, and known as tri-, tetra-, penta-, hexa-, and hepta-methylene, &c., or cyclo- propane, -butane, -pentane, -hexane, -heptane, &c.: - CH 21 CH 2 CH 2 CH2.CH2 CH2 CH2 CH2?C1H,, I I H ?