are compounds composed of carbon and hydrogen are divided
into two classes: aromatic
compounds, which contain benzene and other similar compounds, and
aliphatic compounds (G. aleiphar, fat, oil), which do not.
In aliphatic compounds, carbon atoms can be joined together in straight
chains, branched chains, rather than rings. They can be joined by single
bonds (alkanes), double bonds (alkenes),
or triple bonds (alkynes).
Besides hydrogen, other elements can be bound to the carbon chain, the most
common being oxygen, nitrogen, sulfur,
and chlorine. The simplest aliphatic compound is
methane (CH4). Aliphatics include
alkanes such as
fatty acids and
paraffin
hydrocarbons,
alkenes (such as
ethylene) and
alkynes (such as
acetylene).