Decahydronaphthalene

Decalin
IUPAC name	1,2,3,4,4a,5,6,7,8,8a- decahydronaphthalene
Other names	decalin bicyclo[4.4.0]decane
Identifiers
CAS number	[91-17-8]
SMILES	C1CCC2CCCCC2C1
Properties
Molecular formula	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)
Solubility in water	Insoluble
Hazards
MSDS	Decalin MSDS
Flash point	57 °C
Autoignition temperature	250 °C
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references

Decahydronaphthalene (also known as decalin, or as bicyclo[4.4.0]decane), a bicyclic organic compound, is an industrial solvent. A colorless liquid with an aromatic odor, it is used as a solvent for many resins. 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 organic peroxides upon storage in the presence of air.

Isomers

Decahydronaphthalene occurs in cis and trans forms. The trans form is energetically more stable because of fewer steric interactions.

1: trans (left) and cis (right) isomers

2: ball-and-stick model of cis-decalin

3: trans-decalin

trans decaline

4: Half a declin 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.

References

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