Cycloalkanes:

Cycloalkanes are cyclic alkanes (alicyclic compounds) comprising the general formula C_nH_2n in which the carbon atoms have been connected together to make a ring. All sizes of ring are probable. Tough, the most generally encountered cycloalkane in organic chemistry is the six-membered ring (cyclohexane). Several cycloalkanes are unreactive to chemical reagents. Though, small three- and four-membered rings are reactive and behave such as alkenes. Such types of cyclic structures are extremely strained since it is not possible for the carbon atoms to adopt their preferred tetrahedral shape.