aliphatic compound (ălˌəfătˈĭk) [key], any of a large class of organic compounds whose carbon atoms are joined together in straight or branched open chains rather than in rings. The hydrocarbons of the alkane, alkene, and alkyne series are aliphatic compounds, as are fatty acids and many other compounds. Most compounds containing rings are aromatic compounds; compounds that contain a ring but are not aromatic compounds are called alicyclic.
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