Compounds · Monoterpenes · Terpenoid pathway
α-Pinene
Also known as 2-Pinene — an analysis may use any of these names
Pine, dry, sharp. It evaporates so fast it has usually left before you can name it.
- CAS
- 80-56-8
- Formula
- C10H16
- Molar mass
- 136.23
- Odour threshold
- 100 ppbin water
- Boiling point
- ≈ 155 °C at atmospheric pressure
The two axes are 65 points apart. Volatility tells you whether the compound leaves a surface early or late; the threshold tells you how much of it the nose needs before it notices. When the two sit this far apart, they explain things the percentages on an analysis cannot explain on their own.
About the CAS number and optical isomers
The CAS number above does not specify the optical isomer. Pine oil and holy basil usually lean strongly towards one form rather than being balanced, and the ratio between the two forms is one of the signs that distinguish geographical origin — but it can only be read with a chiral column.
Must be declared on the label
This compound was added by Regulation (EU) 2023/1545 to the list of allergens that must be declared individually on cosmetic labels in the European Union. Name to use on the label: PINENE.
The declaration threshold is 0.001% in leave-on products and 0.01% in rinse-off products. This is an EU requirement — see the regulations page for why it matters beyond the EU. This is not legal advice.
Where it comes from
Biosynthetic pathway: Terpenoid pathway — plants build them from identical five-carbon blocks.
About the threshold figure
High. For the same reason as limonene: monoterpene hydrocarbons generally need large concentrations.
Published thresholds differ by several orders of magnitude, because of differences in measuring method, sample purity and panel. The figure here is an order of magnitude for relative comparison, not a measurement. We give it only for compounds where the literature broadly agrees — 52 of the 106 compounds in the library. The rest are left blank rather than guessed.
Why it sits where it does
A small ten-carbon molecule with no polar group to hold it back. That is why it sits at the far left of the volatility band and leaves a smelling strip almost first.
Where else you meet it
Pine resin, fresh pine wood, and most pine-scented cleaning products. Also present in craft beers that use a lot of hops.