Hiilirunko

Hiilirunko, or carbon skeleton, is a term used in chemistry to describe the arrangement of carbon atoms that forms the main framework of an organic molecule. This skeleton determines the molecule’s size, shape, and degree of branching, and it provides the attachment points for functional groups. In Finnish educational contexts, hiilirunko is distinguished from substituents by focusing on the carbon framework rather than the groups attached to it.

Skeleton types include linear (unbranched chains), branched (iso-alkane type), cyclic (ring structures), and aromatic (conjugated rings such as benzene). The specific pattern of bonds in the hiilirunko affects properties such as boiling point, density, and chemical reactivity, and it influences stereochemistry and isomerism. Functional groups may be added to or removed from the skeleton during reactions, but the skeleton itself defines the core of the molecule.

Representations: Skeletal formulas, often using line-angle drawings, depict only the carbon skeleton and major heteroatoms, with hydrogens implied. In naming, the hiilirunko forms the backbone used in IUPAC nomenclature, where the longest chain or ring is selected and substituents are numbered accordingly.

Examples: The linear skeleton of butane is four connected carbons in a chain; a cyclohexane skeleton is a six-membered carbon ring; benzene represents an aromatic skeleton with alternating double bonds in a ring.

See also: Functional group, Skeletal formula, Isomerism.