Editing Organic chemistry (section)

===Aliphatic compounds===
{{Main|Aliphatic compound}}
The aliphatic hydrocarbons are subdivided into three groups of [[homologous series]] according to their state of [[Saturated and unsaturated compounds|saturation]]:
* [[alkanes]] (paraffins): aliphatic hydrocarbons without any [[Double bond|double]] or [[triple bond]]s, i.e. just C-C, C-H single bonds
* [[alkenes]] (olefins): aliphatic hydrocarbons that contain one or more double bonds, i.e. di-olefins (dienes) or poly-olefins.
* [[alkynes]] (acetylenes): aliphatic hydrocarbons which have one or more triple bonds.
The rest of the group is classified according to the functional groups present.  Such compounds can be "straight-chain", branched-chain or cyclic.  The degree of branching affects characteristics, such as the [[octane number]] or [[cetane number]] in petroleum chemistry.

Both saturated ([[alicyclic]]) compounds and unsaturated compounds exist as cyclic derivatives. The most stable rings contain five or six carbon atoms, but large rings (macrocycles) and smaller rings are common. The smallest cycloalkane family is the three-membered [[cyclopropane]] ((CH<sub>2</sub>)<sub>3</sub>). Saturated cyclic compounds contain single bonds only, whereas aromatic rings have an alternating (or conjugated) double bond. [[Cycloalkane]]s do not contain multiple bonds, whereas the [[cycloalkene]]s and the [[cycloalkyne]]s do.