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Terpenes
Terpenes are volatile organic compounds that plants construct from isoprene subunits. Isoprene is also called 2-methyl-1,3-butadiene, and human chemists use it to make some forms of rubber. Pinene is a monoterpene, meaning it's been formed from two isoprene units. Pinene is also a bicyclic compound, meaning it contains two rings that share carbon atoms. Its molecular formula is C10H16.
Properties
Alpha-pinene has a molecular weight of 136.23 grams per mole. It melts at -80 degrees Fahrenheit and thus is ordinarily found in liquid form, while it boils at 309 degrees F. As you'd expect from its structure, it does not dissolve in water but dissolves rather well in chloroform and ether solvents. Humans use it for paint solvents and coatings and in the manufacture of compounds like camphor and menthol.
Structure
Alpha-pinene is an example of a bridged bicyclic structure, meaning that there are two rings the share two nonadjacent carbon atoms. The alpha form actually has an enantiomer or mirror-image form found in nature. One of the two enantiomers is called the (-) or 1S, 5S form, while the other is the (+) or 1R,5R form. Another nonmirror image form of pinene also found in nature is called beta-pinene. Like alpha-pinene, it has two mirror-image forms.
Considerations
Alpha-pinene has a pine tree-like scent that many people find appealing. As noted in an article from the USDA Forest Service Proceedings, alpha-pinene is toxic for many insects that feed on these trees. Like many volatile oils, it's also quite flammable, which is an important consideration if you're working with large quantities of this compound. The turpentine from which it is normally derived contains a diverse mix of terpenes.