Alkanes

Alkanes are the most basic organic compounds. They are saturated hydrocarbons, which is just a fancy way of saying that they only contain single bonds and they are composed of hydrogens and carbons. Alkanes have a general chemical formula of CnH2n+2, where n equals the number of carbons. They are primarily used in gasoline, lubricating oils, and organic solvents. Some biologically important alkanes include methane and some molecules that make up the waxy coverings on plants.

As well as being the most basic organic compound, alkanes are also the least reactive. This is because each carbon is covalently bound to either four hydrogens, three hydrogens and a carbon, or two hydrogens and two carbons. This uses up all four of the electrons on the carbon atom and the hydrogen atoms that are available in the valency (bonding) shell, leaving no room for other reactions. They are also colorless and odorless. The boiling points and melting points of alkanes are relatively low, however they do increase as you add carbons. The first four alkanes are gases at room temperature and only become solids when there are more than 17 carbons. Alkanes are insoluble in water, they are a polar and are held together in water by weak Van der Waals forces. They can act as solvents for other non-polar molecules.

Structure and orientation of methane

The International Union of Pure and Applied Chemistry (IUPAC) have a standard way of naming all organic compounds. All alkanes are given the suffix ‘-ane’ and a prefix that depends on the amount of carbon atoms. Methane, shown above, has one carbon, ‘meth’, and is an alkane, ‘ane’. The first twelve prefixes are below.

OneMeth-
TwoEth-
ThreeProp-
FourBut-
FivePent-
SixHex-
SevenHept-
EightOct-
NineNon-
TenDec-
ElevenUndec-
TwelveDodec-
IUPAC prefixes
Structure of butane with shorthand structure

Alkanes Alkanes are not particularly biologically active. Methanogenic bacteria produce methane and some long-chain alkanes form protective waxes on some plants and some fungi. The most important biological functions of alkanes are as pheromones, a type of chemical messenger that insects use for communication, such as pentacosane (C25H52)in the pheromones of the beetle Xylotrechus colonus.

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