Compounds · Sesquiterpenes · Terpenoid pathway
β-Bisabolene
Warm spice, slightly citrus, with a balsamic note. Softer than most woody sesquiterpenes.
- CAS
- 495-61-4
- Formula
- C15H24
- Molar mass
- 204.36
- Odour threshold
- —
- Boiling point
- ≈ 274 °C estimated
Where it comes from
Biosynthetic pathway: Terpenoid pathway — plants build them from identical five-carbon blocks.
Why it sits where it does
This is where the shape of a molecule says more than its mass, and it runs against ordinary intuition.
Bisabolene has an open-chain part, so the molecule is spread out, while α-copaene and α-cedrene fold into three tight rings. All three weigh the same, fifteen carbons each. Intuition says the open-chain compound is more mobile and so evaporates more easily, but in practice it is usually the reverse.
The reason is contact surface: a spread-out molecule touches its neighbours at more points, so the total force holding it back is greater. A compact molecule has a smaller surface and escapes more easily even at the same weight.
The boiling points in this group are all estimates, so don’t use them for precise ranking. What is worth remembering is the principle: mass gives you the range, shape decides the position within it.
Where else you meet it
Ginger, lemon, oregano, and many spices. In ginger it accompanies zingiberene and forms the warm part underneath.
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