Cycloalkane
In organic chemistry, the cycloalkanes (also called naphthenes, but distinct from naphthalene) are the monocyclic saturated hydrocarbons. In other words, a cycloalkane consists only of hydrogen and carbon atoms arranged in a structure containing a single ring (possibly with side chains), and all of the carbon-carbon bonds are single. Cycloalkanes are named analogously to their normal alkane counterparts of the same carbon count: cyclopropane, cyclobutane, cyclopentane, cyclohexane, etc. The larger cycloalkanes, with more than 20 carbon atoms are typically called cycloparaffins.
The cycloalkanes without side chains are classified as small (cyclopropane and cyclobutane), common (cyclopentane, cyclohexane, and cycloheptane), medium (cyclooctane through cyclotridecane), and large (all the rest). Each is an isomer of its alkene counterpart—for example, cyclopropane has the same chemical formula (C3H6) as propene.
Besides this standard definition by the International Union of Pure and Applied Chemistry, in some authors' usage the term cycloalkane includes also those saturated hydrocarbons that are polycyclic. In any case, the general form of the chemical formula for cycloalkanes is CnH2(n+1−r), where n is the number of carbon atoms and r is the number of rings.
...
Wikipedia