Compounds · Sesquiterpenes · Terpenoid pathway
α-Humulene
Dry wood, slightly pungent, with a hop note. Lighter in impression than caryophyllene although of similar weight.
- CAS
- 6753-98-6
- Formula
- C15H24
- Molar mass
- 204.36
- Odour threshold
- 120 ppbin water
- Boiling point
- ≈ 275 °C estimated
For this compound the two axes sit close together. Volatility tells you whether it leaves a surface early or late; the threshold tells you how much of it the nose needs before it notices.
Where it comes from
Biosynthetic pathway: Terpenoid pathway — plants build them from identical five-carbon blocks.
About the threshold figure
Moderately high. Several times higher than caryophyllene although the two are isomers.
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
The large-ring isomer of β-caryophyllene — the same formula, a different way of closing the ring. The two almost always occur together in nature, and the ratio between them is fairly stable within a species.
Where else you meet it
Hops, clove, basil, lemongrass. The humulene-to-caryophyllene ratio is a species fingerprint on an analysis.
Dictionary entries that mention this compound
About the boiling-point figure
Boiling points of heavy molecules are often published at reduced pressure without the pressure being stated, because at atmospheric pressure many of them decompose before they boil. The value here is an estimate converted to atmospheric pressure, used to place the compound on the volatility axis, not a measurement. Why this detail matters