In chemistry, an open-chain compound (also spelled as open chain compound) or acyclic compound (Greek prefix "α", ''without'' and "κύκλος", ''cycle'') is a compound with a linear structure, rather than a cyclic one. An open-chain compound having no

side chain In organic chemistry and biochemistry, a side chain is a chemical group that is attached to a core part of the molecule called the "main chain" or backbone. The side chain is a hydrocarbon branching element of a molecule that is attached to a ...

s is called a straight-chain compound (also spelled as straight chain compound). Many of the simple molecules of

organic chemistry Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clay ...

, such as the

alkane In organic chemistry Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms tha ...

s and

alkene In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond. Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...

s, have both linear and ring

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers. ...

s, that is, both acyclic and cyclic, with the latter often classified as

aromatic In chemistry, aromaticity is a chemical property of cyclic (ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to sat ...

. For those with 4 or more carbons, the linear forms can have straight-chain or branched-chain isomers. The lowercase prefix ''n-'' denotes the straight-chain isomer; for example, ''n''-butane is straight-chain

butane Butane () or ''n''-butane is an alkane with the formula C4H10. Butane is a gas at room temperature and atmospheric pressure. Butane is a highly flammable, colorless, easily liquefied gas that quickly vaporizes at room temperature. The name bu ...

, whereas ''i''-butane is isobutane.

Cycloalkane In organic chemistry, the cycloalkanes (also called naphthenes, but distinct from naphthalene) are the monocyclic saturated hydrocarbons. In other words, a cycloalkane consists only of hydrogen and carbon atoms arranged in a structure containin ...

s are isomers of alkenes, not of alkanes, because the ring's closure involves a C-C bond. Having no rings (aromatic or otherwise), all open-chain compounds are

aliphatic In organic chemistry, hydrocarbons ( compounds composed solely of carbon and hydrogen) are divided into two classes: aromatic compounds and aliphatic compounds (; G. ''aleiphar'', fat, oil). Aliphatic compounds can be saturated, like hexane, ...

. Typically in

biochemistry Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology ...

, some isomers are more prevalent than others. For example, in living organisms, the open-chain isomer of glucose usually exists only transiently, in small amounts;

D-glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using ...

is the usual isomer; and L-glucose is rare. Straight-chain molecules are often not literally straight, in the sense that their

bond angle Bond or bonds may refer to: Common meanings * Bond (finance), a type of debt security * Bail bond, a commercial third-party guarantor of surety bonds in the United States * Chemical bond, the attraction of atoms, ions or molecules to form chemi ...

s are often not 180°, but the name reflects that they are

schematic A schematic, or schematic diagram, is a designed representation of the elements of a system using abstract, graphic symbols rather than realistic pictures. A schematic usually omits all details that are not relevant to the key information the s ...

ally straight. For example, the straight-chain alkanes are wavy or "puckered", as the models below show. Nonane 3D ball

References

{{DEFAULTSORT:Open Chain Molecular geometry