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Perhydropyrene, liquid or solid? May 10, 2009

Posted by fetzthechemist in Uncategorized.
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I was looking up the literature for a project/ Perhydropyrene (PHP) is one of the “compounds” of interest. The quotes are there because perhydropyrene as bought from various sources is a crude mixture. Even if it is all perhydropyrene, there are 14 diasteriomers. These correspond to the various chair and boat cyclohexane rings joined in various cis and trans fashion. This is analogous to perhydronaphthalene being cis and trans decalins. The physical and chemical properties of the decalins hints that the PHP isomers ought to each individually behave in a certain fashion. Even the smell of cis-decalin is different than trans-decalin!

The commercial sources of PHP all derive from two types of PHP, each obtained once upon a time, by different hydrogenation methods (catalysts, temperatures, hydrogen pressure differences). Both have predominantly five to eight of the 14 possible isomers. This mixture leads to both samples being oily liquids.

Since the PHP isomers differ in 3-D shape, they do not effectively layer up against each other. This leads to them not forming good quasicrystalline solids. Thus, the oils are the form. If you do different molecular separations, you can isolate small amounts of PHP isomer – or at least those half-dozen or so that are the bulk of the sample. Each of those is a nice clear or whitish crystalline solid.

This is similar behavior to certain hydrocarbon oils. Mixtures of long-chain n-alkanes in the range of thirty to fifty carbons are oils, even when the individual constituents are each a solid wax.

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