Aliphatic

Aliphatic refers to organic compounds whose carbon framework is not aromatic. It encompasses open-chain molecules such as alkanes, alkenes, and alkynes, as well as non-aromatic cyclic compounds (cycloalkanes and cycloalkenes). The term is used to distinguish these non-aromatic carbon frameworks from aromatic compounds, which contain conjugated ring systems with delocalized pi electrons. Aliphatic compounds can be purely hydrocarbon or bear heteroatoms appended to the carbon skeleton, yielding classes such as aliphatic alcohols, amines, sulfides, and ethers. In many contexts, aliphatic also describes fats, oils, and lipid-like substances when they are not based on aromatic ring systems.

Classification and properties: Alkanes are saturated; alkenes and alkynes are unsaturated. Cycloalkanes are non-aromatic rings. Aliphatic molecules tend to be nonpolar or only weakly polar, with limited water solubility and greater affinity for nonpolar solvents. Reactions commonly associated with aliphatic chemistry include radical halogenation of alkanes, addition to alkenes and alkynes, oxidation of alcohols, substitution and condensation reactions, and polymerization of unsaturated hydrocarbons. The term is widely used in chemistry, biochemistry, and environmental science to describe non-aromatic carbon frameworks, including the long hydrocarbon chains of many lipids and the aliphatic side chains of several amino acids (as opposed to the aromatic residues phenylalanine, tyrosine, tryptophan).