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 (in which all the C-C bonds are single requiring the structure to be completed, or 'saturated', by hydrogen) 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]

Acyclic aliphatic/non-aromatic compound (butane)
Cyclic aliphatic/non-aromatic compound (cyclobutane)

Structure edit

Aliphatic compounds can be saturated, joined by single bonds (alkanes), or unsaturated, with double bonds (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 edit

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 of aliphatic compounds edit

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   Alkane
C2H2 Acetylene   Alkyne
C2H4 Ethylene   Alkene
C2H6 Ethane   Alkane
C3H4 Propyne   Alkyne
C3H6 Propene   Alkene
C3H8 Propane   Alkane
C4H6 1,2-Butadiene   Diene
C4H6 1-Butyne   Alkyne
C4H8 1-Butene   Alkene
C4H10 Butane   Alkane
C6H10 Cyclohexene   Cycloalkene
C5H12 n-pentane   Alkane
C7H14 Cycloheptane   Cycloalkane
C7H14 Methylcyclohexane   Cyclohexane
C8H8 Cubane   Prismane, Platonic hydrocarbon
C9H20 Nonane   Alkane
C10H12 Dicyclopentadiene   Diene, Cycloalkene
C10H16 Phellandrene    Terpene, Diene, Cycloalkene
C10H16 α-Terpinene   Terpene, Diene, Cycloalkene
C10H16 Limonene    Terpene, Diene, Cycloalkene
C11H24 Undecane   Alkane
C30H50 Squalene   Terpene, Polyene
C2nH4n Polyethylene   Alkane

References edit

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