Alkanes are hydrocarbons that contain only single bonds.
When carbons double back on one another to form a ring, they are called cycloalkanes . Alkanes are generally unreactive, and have the purpose of holding reactive functional groups , or the nonalkane portion of a molecule. Since we generally don't care about the non-reactive portions of molecules, Organic Chemists often use the symbol R to represent alkyl substituents. Naming of organic structures, unlike biological classification, follows a rigid set of rules. However, common names of compounds, or names that have historical roots, are still used today for many compounds.