Decalin a bicyclic organic compound

Organic compound

An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...

, is an industrial solvent

Solvent

A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...

. A colorless liquid with an aromatic odor, it is used as a solvent for many resin

Resin

Resin in the most specific use of the term is a hydrocarbon secretion of many plants, particularly coniferous trees. Resins are valued for their chemical properties and associated uses, such as the production of varnishes, adhesives, and food glazing agents; as an important source of raw materials...

s or fuel additive. It is the saturated analog of naphthalene

Naphthalene

Naphthalene is an organic compound with formula . It is a white crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 ppm by mass. As an aromatic hydrocarbon, naphthalene's structure consists of a fused pair of benzene rings...

 and can be prepared from it by hydrogenation

Hydrogenation

Hydrogenation, to treat with hydrogen, also a form of chemical reduction, is a chemical reaction between molecular hydrogen and another compound or element, usually in the presence of a catalyst. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically...

 in a fused state in the presence of a catalyst. Decahydronaphthalene easily forms explosive organic peroxide

Organic peroxide

Organic peroxides are organic compounds containing the peroxide functional group . If the R' is hydrogen, the compound is called an organic hydroperoxide. Peresters have general structure RCOOR. The O-O bond easily breaks and forms free radicals of the form RO·...

s upon storage in the presence of air.

Isomers

Decahydronaphthalene occurs in cis and trans forms

Geometric isomerism

In organic chemistry, cis/trans isomerism or geometric isomerism or configuration isomerism or E/Z isomerism is a form of stereoisomerism describing the orientation of functional groups within a molecule...

. The trans form is energetically more stable because of fewer steric interactions. Cis-decalin is a chiral molecule without chiral center; it has a two-fold rotational symmetry axis going through the center of 1-6 bond but no reflective symmetry. However, the chirality

Chirality (chemistry)

A chiral molecule is a type of molecule that lacks an internal plane of symmetry and thus has a non-superimposable mirror image. The feature that is most often the cause of chirality in molecules is the presence of an asymmetric carbon atom....

 is canceled through a chair flipping process that turns the molecule into its mirror image.

Trans decaline

As can be seen on the model of cyclohexane

Cyclohexane

Cyclohexane is a cycloalkane with the molecular formula C6H12. Cyclohexane is used as a nonpolar solvent for the chemical industry, and also as a raw material for the industrial production of adipic acid and caprolactam, both of which being intermediates used in the production of nylon...

, the trans configuration comes with a price: the only possible way to join the two six membered rings in trans relation will mean the second ring needs to start out of two equatorial bonds of the first ring. A six membered ring does not offer space enough to start out on an axial position (say up), and reach for the axial position of the carbon atom next door, which then will be on the down side of the molecule.

A second price to be paid is the effective freezing of the rings in a fixed conformation. In biology

Biology

Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...

 this fixation is widely used in the steroid

Steroid

A steroid is a type of organic compound that contains a characteristic arrangement of four cycloalkane rings that are joined to each other. Examples of steroids include the dietary fat cholesterol, the sex hormones estradiol and testosterone, and the anti-inflammatory drug dexamethasone.The core...

 skeleton to construct molecule

Molecule

A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...

s that play a key role in the signaling between far separated cells.