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Alkanes: Structure and Constitution

Alkanes: Constitution and Nomenclature

Historically based, the first four n-alkanes have nonsystematic names: Methane, ethane, propane, and butane. The higher members are named systematically with a Greek-related numerical index and with the ending -ane to classify the compounds as hydrocarbons.

The basic fundamentals for the naming of molecules are summarized on the page link ist im inline-mode noch nicht implementiert."IUPAC-nomenclature".

NamenNotationStructureAbbreviated notation
Methane1 CH4
Ethane2 CH3-CH3
Propane3 CH3-CH2-CH3
Butane4 CH3-CH2-CH2-CH3
Pentane5 CH3-(CH2)3-CH3
Hexane6 CH3-(CH2)4-CH3
n-Paraffins20-30 CH3-(CH2)20-30-CH3
Polyethylene5000-106 CH3-(CH2)5000-CH3

Higher alkanes with about 20-30 carbon atoms are called n-paraffins. The name is derived from the Latin parum, little, and affinum, affined, indicating that paraffins show low reactivity and do not mix with water.

Mostly, the structural formulae of alkanes are not explicitly written by including all element symbols. For simplication purposes, even the hydrogen atoms are omitted and the structure is written as a zig-zag line or as a graph in the case of branched or cyclic alkanes. The corner of the graphs represent carbon atoms and the edges correspond to C-C single bonds. Hydrogen atoms are virtually added until the four valences of the carbon atoms are satisfied. This procedure provides a much clearer picture of complex formulae.

Groups of molecules which are connected by a single bond can usually rotate around this bond. Each position the groups take up in relation to each other is called the conformation of the molecule.

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