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 monocyclic cycloalkanes: cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, and so on. Bicyclic alkanes include bicycloundecane and decalin. Polycyclic alkanes include cubane, basketane, and housane.
Spiro compounds have two or more rings that are connected through only one carbon atom.
The mode of ring-closing in the formation of many alicyclic compounds can be predicted by Baldwin's rules.
Two more examples are shown below, on the left methylenecyclohexane and on the right 1-methylcyclohexene:
An exocyclic group is always shown outside the ring structure, take for instance the exocyclic double bond of the former molecule. Isotoluenes are a prominent class of compounds with exocyclic double bonds.
The placement of double bonds in many alicyclic compounds can be predicted with Bredt's rule.