Aliphatic compound

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. 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. These criteria are not present in the current IUPAC definition.

Aliphatic compounds can be saturated, i.e. alkanes (single carbon-carbon bonds), or unsaturated, with carbon-carbon double (alkenes) or triple bonds (alkynes). It may also be cyclic (as long as it is not aromatic).

Under definitions which require that aliphatic compounds are strictly hydrocarbons, the addition of other elements beyond carbon and hydrogen (heteroatoms) makes the compound no longer aliphatic. Nevertheless, such compounds are sometimes still 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).

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.

A few examples of aliphatic compounds is listed below (sorted by the number of carbon-atoms).