Aliphatic hydrocarbons

Cyclohexane , an aliphatic

Aliphatic hydrocarbons ( ancient Greek ἄλειφαρ aleiphar 'fatty') are organic chemical compounds that are composed of carbon and hydrogen and are not aromatic . This makes them a subgroup of hydrocarbons . According to the IUPAC nomenclature, aliphatic compounds are “ acyclic or cyclic , saturated or unsaturated carbon compounds, with the exception of aromatic compounds.” The simplest group of aliphatic hydrocarbons are the saturated alkanes ; Furthermore, the likewise saturated cycloalkanes and the unsaturated hydrocarbons of the alkenes and alkynes belong to the group of aliphatics.

Like all pure hydrocarbons, aliphatic hydrocarbons are non-polar, lipophilic compounds (i.e. not water-soluble). Since, according to the IUPAC definition, aliphatic compounds are opposed to aromatic carbon compounds and thus defined by a negation, this means, conversely, that all non- aromatic organic compounds are aliphatic. The classification of organic compounds into aliphatics and aromatics is based on the aromaticity criteria . The so-called alicyclic compounds form a subgroup of the aliphatics and are characterized - similar to the aromatics - by ring-shaped chains, but are distinguished from the aromatics by the aromaticity criteria.

Exemplary aliphatic compounds

The most important groups of substances of aliphatic compounds according to the above definition are:

• n -alkanes, iso- alkanes and cycloalkanes (saturated hydrocarbons),
• straight-chain, branched and cyclic alkenes (unsaturated hydrocarbons) and
• Alkynes (also unsaturated hydrocarbons).

Important examples of aliphatic compounds can be found in the following table (arranged according to the increasing number of carbon or hydrogen atoms):

formula	Surname	CAS number	Structural formula	Substance group	Synonyms
CH 4	methane	74-82-8		Alkane	-
C 2 H 2	Ethine	74-86-2		Alkyne	Ethine, acetylene, acetylene
C 2 H 4	Ethene	74-85-1		Alkene	Ethylene, ethene, ethylene, Elaylgas, vinyl hydrogen, etherin, acetane, R 1150
C 2 H 6	Ethane	74-84-0		Alkane	Ethane
C 3 H 4	Propyne	74-99-7		Alkyne	Methyl acetylene, allylene
C 3 H 6	Propene	115-07-1		Alkene	Propylene
C 3 H 8	propane	74-98-6		Alkane
C 4 H 6	1,2-butadiene	590-19-2		Service	Buta-1,2-diene, methylallene
C 4 H 6	1-butyne	107-00-6		Alkyne	Ethyl acetylene
C 4 H 8	Butene	-	z. B.	Alkene	Butylene
C 4 H 10	n -Butane	106-97-8		Alkane
C 5 H 12	n -pentane	109-66-0		Alkane	Amyl hydride
C 6 H 10	Cyclohexene	110-83-8		Cycloalkene	1,2,3,4-tetrahydrobenzene
C 7 H 14	Cycloheptane	291-64-5		Cycloalkane	Heptamethylene
C 7 H 14	Methylcyclohexane	108-87-2		Cycloalkane	Hexahydrotoluene, cyclohexyl methane
C 8 H 8	Cuban	277-10-1			Pentacyclo [4.2.0.0 2.5 .0 3.8 .0 4.7 ] octane
C 9 H 20	Nonane	111-84-2		Alkane	n -Nonan
C 10 H 12	Dicyclopentadiene	77-73-6		Diene, cycloalkene	3a, 4,7,7a-Tetrahydro-4,7-methanoindene, tricyclo [5.2.1.0 2,6 ] deca-3,8-diene, TCD, DCPD, dimeric cyclopentadiene
C 10 H 16	Phellandras	99-83-2		Terpene, diene, cycloalkene	α-Phellandrene: 2-methyl-5- (1-methylethyl) -1,3-cyclohexadiene, β-Phellandrene: 3-methylene-6- (1-methylethyl) cyclohexene
C 10 H 16	α-terpinene	99-86-5		Terpene, cycloalkene, diene	Mentha-1,3-diene, 1-isopropyl-4-methyl-1,3-cyclohexadiene
C 10 H 16	Limes	5989-27-5		Terpene, diene, cycloalkene	1-methyl-4-prop-1-en-2-ylcyclohexene, Carven, p-mentha-1,8-diene, 1-methyl-4-isopropenyl-1-cyclohexene, 1-methyl-4- (1-methylethenyl ) cyclohexene, 4-isopropenyl-1-methylcylohexene, dipentene, rubber, cinen, cajeputene
C 11 H 24	Undecane	1120-21-4		Alkane	Undecan, n -Undecan, n -Undecan, Hendekan
C 30 H 50	Squalene	111-02-4		Terpene, polyene	2,6,10,15,19,23-hexamethyl- 2,6,10,14,18,22-tetracosahexaene, spinacene, supraen
C 2n H 4n	Polyethylene	9002-88-4		Alkane	Polyethene, PE

Aliphatic compounds in spectroscopy

Aliphatic CH stretching vibrations of non- conjugated CH units in a molecule have characteristic peaks in the IR spectrum in the range from 3000 to 2750 cm ⁻¹ . In contrast, the peaks in conjugated CH units are beyond the 3000 cm ⁻¹ limit.

In ¹ H- NMR spectrum, most aliphatic peaks in the range of 1-2 ppm are. Higher values ​​up to about 5 ppm are obtained for adjacent electron withdrawing groups.

Aliphatic compounds in petrochemicals

The main source of aliphatic compounds is petroleum. The most important method of oil processing is steam cracking , in which u. a. Ethane , LPG , naphtha and gas oil or other suitable hydrocarbons can be cracked. The gas phase of the steam cracker products contains the basic aliphatic chemicals ethylene , propylene , the C4 cut (mainly butene , isobutene and 1,3-butadiene ) and isoprene .

The most important aliphatic by-products from this are made from the substances eth (yl) en, prop (yl) en and but (yl) en. There are:

• from ethylene :
  • Polyethylene - e.g. B. Ziegler-Natta method
    • approx. 21% of the total ethylene production in LDPE
    • approx. 13% as LLDPE
    • approx. 23% as HDPE
  • α-olefins
    • Poly-α-olefins as lubricants
    • Co-monomers for polyethylene
• made of propylene :
  • Polypropylene - e.g. B. by Ziegler-Natta process (approx. 57% of the total propylene production)
• from butene :
  • Monomers and co-monomers (butene derived products in plastics production )
  • Isobutene - as a monomer for copolymerization with isoprene
  • 1,3-butadiene - monomer or co-monomer for polymerisation into elastomers

Web links

• Glossary of Class Names of Organic Compounds and Reactive Intermediates Based on Structure (IUPAC Recommendations 1994): "Acyclic Hydrocarbons" , Department of Chemistry, Queen Mary University of London.

Individual evidence

1. ^ Aliphatic compounds. (PDF; 4 kB) 2nd Edition. (No longer available online.) IUPAC Compendium of Chemical Terminology, 1997, archived from the original on November 14, 2013 ; accessed on June 14, 2020 (English). 
2. ↑ ChemgaPedia steam cracking .