Decalin

Decalin (decahydronaphthalene, also known as bicyclodecane and sometimes decaline), 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 additives. It is the saturated analog of naphthalene and can be prepared from it by hydrogenation in the presence of a catalyst. Decahydronaphthalene easily forms explosive organic peroxides upon storage in the presence of air. Decalin (decahydronaphthalene, also known as bicyclodecane and sometimes decaline), 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 additives. It is the saturated analog of naphthalene and can be prepared from it by hydrogenation in the presence of a catalyst. Decahydronaphthalene easily forms explosive organic peroxides upon storage in the presence of air. 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 a chiral center; it has a two-fold rotational symmetry axis going through the center of the 9–10 bond, but no reflective symmetry. However, the chirality is canceled through a chair-flipping process that turns the molecule into its mirror image. The only possible way to join the two six-membered rings in the trans position means the second ring needs to start from two equatorial bonds (blue) of the first ring. A six-membered ring does not offer sufficient space to start out on an axial position (upwards), and reach the axial position of the neighboring carbon atom, which then will be on the downwards side of the molecule (see the model of cyclohexane in figure 5). The structure is conformationally frozen, rather than having the ability to undergo the chair flip as in the cis isomer. In biology this fixation is widely used in the steroid skeleton to construct molecules (such as figure 6) that play a key role in the signalling between distantly separated cells.