Chemistry:Aliphatic compound

Short description: Hydrocarbon compounds without aromatic rings

Acyclic aliphatic/non-aromatic compound (butane)

thumb|right|170px|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 (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.

Structure

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

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

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
CH 4	Methane		Alkane
C 2H 2	Acetylene		Alkyne
C 2H 4	Ethylene		Alkene
C 2H 6	Ethane		Alkane
C 3H 4	Propyne		Alkyne
C 3H 6	Propene		Alkene
C 3H 8	Propane		Alkane
C 4H 6	1,2-Butadiene		Diene
C 4H 6	1-Butyne		Alkyne
C 4H 8	1-Butene		Alkene
C 4H 10	Butane		Alkane
C 6H 10	Cyclohexene		Cycloalkene
C 5H 12	n-pentane		Alkane
C 7H 14	Cycloheptane		Cycloalkane
C 7H 14	Methylcyclohexane		Cyclohexane
C 8H 8	Cubane		Prismane, Platonic hydrocarbon
C 9H 20	Nonane		Alkane
C 10H 12	Dicyclopentadiene		Diene, Cycloalkene
C 10H 16	Phellandrene	50px	Terpene, Diene, Cycloalkene
C 10H 16	α-Terpinene		Terpene, Diene, Cycloalkene
C 10H 16	Limonene		Terpene, Diene, Cycloalkene
C 11H 24	Undecane		Alkane
C 30H 50	Squalene		Terpene, Polyene
C 2nH 4n	Polyethylene		Alkane