An alicyclic compound is an organic compound in which carbon atoms are linked to form one or more rings. Aromatic compounds are excluded because of their special properties. In general, alicyclic compounds resemble analogous aliphatic compounds. However, strain occurs in small rings (with three, four, or five members) because the angles between adjacent bonds are less than the preferred angle of 109° 28', and these compounds are less stable and more reactive. Larger rings are nonplanar and unstrained. Cyclohexan (C6H12) is alicyclic, as are many terpenes, such as menthol. See also heterocyclic compound.