Aliphatic compounds (/ˌælɪˈfætɪk/; G. aleiphar, fat, oil) are chemical compounds containing the element carbon that are not aromatic compounds.[1] Aliphatic compounds can be saturated, where all C-C bonds are single bonds (e.g., hexane), or unsaturated, where double or triple bonds are present between carbon atoms (e.g., hexene, hexyne).
Other definitions
The definition given above is that promulgated by the International Union of Pure and Applied Chemistry (IUPAC), which sets accepted definitions for chemical terms and nomenclature.[1] Other sources have previously applied additional restrictions, such as stating that only hydrocarbons (compounds made of only carbon and hydrogen) can be aliphatic or excluding cyclic compounds from being aliphatic.[2][3] These criteria are not present in the current IUPAC definition.
Structure
Aliphatic compounds can be saturated, joined by single bonds (alkanes), or unsaturated, with double (alkenes) or triple bonds (alkynes). If other elements (heteroatoms) are bound to the carbon chain, the most common being oxygen, nitrogen, sulfur, and chlorine, it is no longer a hydrocarbon, and therefore no longer an aliphatic compound. However, such compounds may still be referred to as aliphatic if the hydrocarbon portion of the molecule is aliphatic, e.g. aliphatic amines, to differentiate them from aromatic amines.
The least complex aliphatic compound is methane (CH4).
Properties
Most aliphatic compounds are flammable, allowing the use of hydrocarbons as fuel, such as methane in natural gas for stoves or heating; butane in torches and lighters; various aliphatic (as well as aromatic) hydrocarbons in liquid transportation fuels like petrol/gasoline, diesel, and jet fuel; and other uses such as ethyne (acetylene) in welding.
Examples
The most important[according to whom?] 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 |  | Alkane |
| C2H2 | Acetylene |  | Alkyne |
| C2H4 | Ethylene |  | Alkene |
| C2H6 | Ethane |  | Alkane |
| C3H4 | Propadiene |  | Diene |
| C3H4 | Propyne |  | Alkyne |
| C3H6 | Propylene |  | Alkene |
| C3H8 | Propane |  | Alkane |
| C4H6 | 1,2-Butadiene |  | Diene |
| C4H6 | 1-Butyne |  | Alkyne |
| C4H8 | 1-Butene |  | Alkene |
| C4H10 | Butane | | Alkane |
| C5H12 | Pentane |  | Alkane |
| C6H10 | Cyclohexene |  | Cycloalkene |
| C6H12 | Cyclohexane |  | Cycloalkane |
| C6H14 | Hexane |  | Alkane |
| C7H14 | Methylcyclohexane |  | Cycloalkane |
| C8H8 | Cubane |  | Prismane, Platonic hydrocarbon |
| C8H18 | Octane |  | Alkane |
| C10H12 | Dicyclopentadiene |  | Diene, Cycloalkene |
| C10H16 | Terpinene |   | Terpene, Diene, Cycloalkene |
| C10H16 | Phellandrene |   | Terpene, Diene, Cycloalkene |
| C10H16 | Limonene |   | Terpene, Diene, Cycloalkene |
| C10H22 | Decane |  | Alkane |
| C30H50 | Squalene |  | Terpene, Polyene |
| C2nH4n | Polyethylene |  | Alkane |
References
- 1 2 IUPAC, Compendium of Chemical Terminology, 5th ed. (the "Gold Book") (2025). Online version: (1995) "aliphatic compounds". doi:10.1351/goldbook.A00217
- ↑ Hampel (1992). Glossary of Chemical Terms (2nd ed.). p. 11.
- ↑ Hackh's Chemical Dictionary (5th ed.). 1987. p. 22.
