(also cycloalkane), a saturated cyclic hydrocarbon with the general formula C_nH_2n (seeALICYCLIC COMPOUNDS). The ring of the simplest cycloparaffin, cyclopropane, consists of three methylene, CH₂, groups, and its closest homologue, cyclobutane, consists of four methylene groups, and so forth, as a result of which unsubstituted cycloparaffins are often called polymethylene hydrocarbons, or polymethylenes. Thus, cyclopentane, C₅H₁₀, is also called pentamethylene, while cyclohexane, C₆H₁₂, is called hexamethylene. Cyclopentane and cyclohexane, together with their alkyl derivatives, are components of petroleum and thus are often also called napthenes.

In their physical and chemical properties, cycloparaffins are similar to saturated acyclic hydrocarbons of the methane series. An exception is cyclopropane, which in several reactions behaves like an unsaturated hydrocarbon. Cycloparaffins may be produced by various methods. One method involves the splitting of halogen atoms from dihaloderivatives of hydrocarbons, in whose molecules the halogen atoms are located at the carbons in the 1, 3, 1, 4, 1, 5, . . . positions. Another method involves the dry distillation of calcium salts of dibasic carboxylic acids; the cyclic ketones that form in the process are then reduced to cycloparaffins. Cyclohexane and alkylcyclohexanes are synthesized by the hydrogenation of benzene and its homologues over nickel, platinum, or palladium.