Alkyl Group

Aliphatic compounds, of which the alkanes are one example, have an open chain of carbon atoms as a skeleton. This open chain may be straight or branched. Alkanes, also known as paraffins, are composed of carbon and hydrogen only; they have the generic formula C_nH_2n+2, and are the simplest and least reactive of the aliphatic compounds. Alkanes with straight chains are known as normal alkanes. (Branched chain alkanes are treated as alkyl derivatives of the straight chain compounds.) The first four members of the normal alkane series are methane, ethane, propane, and butane (see below). The names of the remaining normal alkanes are composed of a prefix that indicates the number of carbon atoms in the compound, followed by the termination - ane. Thus, n-hexane is the name given to the normal alkane having a chain of six carbon atoms.

The n-alkanes exist on a continuum that extends from simple gases to molecules of very high molecular weights. The physical properties and uses of the n-alkane change with the number of repeating CH₂ units in the chain. For example, compounds with one to four CH₂ units in the chain are simple gases (e.g. cooking gas) at room temperature; compounds with five to 11 CH₂ units in the chain are simple liquids (e.g. gasoline) at room temperature; compounds with 16 to 25 CH₂ units in the chain are high viscosity liquids (e.g. oil) at room temperature; and compounds with 1,000 to 3,000 CH₂ units in the chain are tough plastic solids (e.g. polyethylene bottles) at room temperature.