Decalin
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| Names | |
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| IUPAC names
1,2,3,4,5,6,7,8,9,10-
decahydronaphthalene | |
| Other names
decalin
bicyclo[4.4.0]decane | |
| Identifiers | |
3D model (JSmol)
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| ChemSpider | |
| ECHA InfoCard | 100.001.861 |
CompTox Dashboard (EPA)
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| Properties | |
| C10H18 | |
| Molar mass | 138.25 g/mol |
| Appearance | Clear, colorless liquid |
| Density | 0.896 g/cm³ |
| Melting point | racemate: −40 °C (−40 °F) trans: −31 °C (−23 °F) cis: −43 °C (−45 °F) |
| Boiling point | trans: 187 °C (369 °F) cis: 196 °C (384 °F) |
| Insoluble | |
| Hazards | |
| Flash point | 57 °C |
| Related compounds | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Decalin (decahydronaphthalene, also known as bicyclo[4.4.0]decane)[1], a bicyclic organic compound, is an industrial solvent. A colorless liquid with an aromatic odor, it is used as a solvent for many resins or fuel additive.[2] It is the saturated analog of naphthalene and can be prepared from it by hydrogenation in a fused state in the presence of a catalyst. Decahydronaphthalene easily forms explosive[3] organic peroxides upon storage in the presence of air.[4][5]
Isomers
Decahydronaphthalene occurs in cis and trans forms. 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 is canceled through a chair flipping process that turns the molecule into its mirror image.
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1: trans (left) and cis (right) isomers -
2:ball-and-stick model of cis-decalin -
3:trans-decalin
Trans decaline
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4: Half a decalin molecule: cyclohexane in chair conformation. Axial positions are shown in red, while those in equatorial positions are in blue. -
5: Androstanediol, a biomolecule with three trans fused six membered rings (and an also trans fused five membered one)
As can be seen on the model of cyclohexane, 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 this fixation is widely used in the steroid skeleton to construct molecules that play a key role in the signaling between far separated cells.