In organic chemistry
, compounds composed of carbon
are divided into two classes: aromatic
compounds, which contain benzene
rings or similar rings of atoms, and aliphatic compounds
, fat, oil), which do not contain aromatic rings.
In aliphatic compounds, carbon atoms can be joined together in straight chains, branched chains, or non-aromatic rings (in which case they are called alicyclic). 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).
Most aliphatic compounds are flammable, allowing the use of hydrocarbons as fuel, such as methane in Bunsen burners, and acetylene in welding.