Class of chemical compounds without aromatic ring
Acyclic aliphatic/non-aromatic compound (butane)
Cyclic aliphatic/non-aromatic compound (cyclobutane)

In organic chemistry, hydrocarbons (compounds composed solely of carbon and hydrogen) are divided into two classes: aromatic compounds and aliphatic compounds (/ˌælɪˈfætɪk/; G. aleiphar, fat, oil). Aliphatic compounds can be saturated, like hexane, or unsaturated, like hexene and hexyne. Open-chain compounds, whether straight or branched, and which contain no rings of any type, are always aliphatic. Cyclic compounds can be aliphatic if they are not aromatic.[1]


Aliphatic compounds can be saturated, joined by single bonds (alkanes), or unsaturated, with double bonds (alkenes) or triple bonds (alkynes). Besides hydrogen, other elements can be bound to the carbon chain, the most common being oxygen, nitrogen, sulfur, and chlorine.

The least complex aliphatic compound is methane (CH4).


Most aliphatic compounds are flammable, allowing the use of hydrocarbons as fuel, such as methane in Bunsen burners and as liquefied natural gas (LNG), and ethyne (acetylene) in welding.

Examples of aliphatic compounds / non-aromatic

The most important aliphatic compounds are:

  • n-, iso- and cyclo-alkanes (saturated hydrocarbons)
  • n-, iso- and cyclo-alkenes and -alkynes (unsaturated hydrocarbons).

Important examples of low-molecular aliphatic compounds can be found in the list below (sorted by the number of carbon-atoms):

Formula Name Structural formula Chemical classification
CH4 Methane Methane-2D-stereo.svg Alkane
C2H2 Acetylene Ethyne-2D-flat.png Alkyne
C2H4 Ethylene Ethene structural.svg Alkene
C2H6 Ethane Ethan Lewis.svg Alkane
C3H4 Propyne Propyne-2D-flat.png Alkyne
C3H6 Propene Propen21.PNG Alkene
C3H8 Propane Propane-2D-flat.png Alkane
C4H6 1,2-Butadiene Buta-1,2-dien.svg Diene
C4H6 1-Butyne Ethylacetylene.svg Alkyne
C4H8 1-Butene But-1-ene-2D-skeletal.png Alkene
C4H10 Butane Butane-2D-flat.png Alkane
C6H10 Cyclohexene Cyclohexen - Cyclohexene.svg Cycloalkene
C5H12 n-pentane Pentan Skelett.svg Alkane
C7H14 Cycloheptane Cycloheptane.svg Cycloalkane
C7H14 Methylcyclohexane Methylcyclohexane.png Cyclohexane
C8H8 Cubane Cuban.svg Octane
C9H20 Nonane Nonan Skelett.svg Alkane
C10H12 Dicyclopentadiene Di-Cyclopentadiene ENDO & EXO V.2.svg Diene, Cycloalkene
C10H16 Phellandrene Phellandrene alpha.svgPhellandrene beta.svg Terpene, Diene Cycloalkene
C10H16 α-Terpinene Alpha-Terpinene Structure V.1.svg Terpene, Cycloalkene, Diene
C10H16 Limonene (R)-Limonen.svg(S)-Limonen.svg Terpene, Diene, Cycloalkene
C11H24 Undecane Undecan Skelett.svg Alkane
C30H50 Squalene Squalene.svg Terpene, Polyene
C2nH4n Polyethylene Polyethylene repeat unit.svg Alkane


  1. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (1995) "aliphatic compounds". doi:10.1351/goldbook.A00217