An alicyclic compound is an organic compound that is both aliphatic and cyclic. They contain one or more all-carbon rings which may be either saturated or unsaturated, but do not have aromatic character. Alicyclic compounds may have one or more aliphatic side chains attached. The simplest alicyclic compounds are the 1. monocyclic cycloalkanes: cyclopropane, cyclobutane, cyclopentane, cyclohexane, cyclohepta ne, cyclooctane, and so on. 2. Bicyclic alkanes include bicycloundecane, decalin, and housane. 3. Polycyclic alkanes include cubane, basketane, and tetrahedrane. Spiro compounds have two or more rings that are connected through only one carbon atom. Nomenclature Cyclic aliphatic hydrocarbons are named by prefixing cyclo- to the name of the corresponding open-chain hydrocarbon having the same number of carbons as the ring. For example: Cyclopropane Cyclobutane Cyclopentane Cyclopentene Substituents on the ring- alkyl, groups, halogens- are named and their positions indicated by numbers. Chlorocyclopropane 1,1- Dimethylyclopentane 1,3-Dimethylcyclohexane CH3 CH3 Cl H3C CH3 In simple cycloalkenes and cycloalkynes the double and triply bonded carbons are considered to occupy positions 1 and 2. For example: 3-Ethylcyclopentene 1,3-Cyclohexadiene H3C For convenience, aliphatic rings are often represented by simple geometric figures: a triangle for cyclopropane, a square for cyclobutane, a pentagon for cyclopentane, a hexagon for cyclohexane and so on. It is understood that two hydrogens are located at each corner of the figure unless some other group is indicated. For example H3C cyclopentane 3-Ethylcyclopentene 1,3-Cyclopentadiene CH3 CH3 Cl CH Cyclohexane 3 1,3-Dimethylcyclohexane 2- Chloro-1-methylcyclohexane As usual alcohols are given the ending –ol, which takes priority over –ene and appears last in the name. The –OH group is considered to be attached to position one. OH OH OH OH Cyclopentanol 3-Cyclohexenol 1,2-Cyclohexanediol Polycyclic compounds contains two or more rings that share two or more carbon atoms. We can illustrate the naming system with norborane, whose systematic name is bicycle [2,2,1] heptane: (a) heptane since it contains contains a total of seven carbon atoms (b) bicylo, since it contains two rings, that is, breaking two carbon to carbon bonds converts it into an open chain compound (c) [2,2,1], since the number of carbons between bridgeheads (shared carbons) is two (C-2 and C- 3), two (C-5 and C-6), and one (C-7). Reference material Organic chemistry 7th Ed. Robert Morrison, Robert Boyd and Saibal Bhattacharjee .