In organic chemistry, hydrocarbons (compounds composed of carbon and hydrogen) are divided into two classes: aromatic compounds and aliphatic compounds (; G. aleiphar, fat, oil) also known as non-aromatic compounds. Aromatic compounds contain an aromatic-ring configuration of atoms, such as benzene, whereas aliphatic compounds do not. Aliphatic compounds can be saturated, like hexane, or unsaturated, like hexene.