Compounds · Ketones · Terpenoid pathway
Carvone
Depending on the isomer it is two unrelated smells: the R form gives spearmint, the S form caraway and dill seed.
- CAS
- 99-49-0
- Formula
- C10H14O
- Molar mass
- 150.22
- Odour threshold
- 10 ppbin water
- Boiling point
- ≈ 231 °C at atmospheric pressure
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.
About the CAS number and optical isomers
The CAS number above does not specify the optical isomer. The two forms have their own numbers: (R)-(−)-carvone is 6485-40-1, and (S)-(+)-carvone is 2244-16-8.
For this compound, which number an analysis gives is not a formality. Routine gas chromatography gives a single peak whichever form the sample is, so an analysis reading “carvone 55%” does not tell you whether you are holding spearmint or caraway. To know, you have to run a chiral column.
That is also why carvone is the classic example used when teaching chiral chromatography.
Where it comes from
Biosynthetic pathway: Terpenoid pathway — plants build them from identical five-carbon blocks.
About the threshold figure
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 ketone on the p-menthane skeleton — the same skeleton as limonene, with just a carbonyl group added in the ring. That group lifts the boiling point from limonene’s 176 degrees to 231, fifty-five degrees apart because of a single oxygen atom.
This is the compound in which the difference between two optical isomers has the clearest consequence in the whole library. With menthol, both forms give a cooling sensation, differing only in strength. With carvone, the two forms give two smells nobody would put side by side judging by nose alone: one is spearmint, the other caraway seed.
The same formula, the same mass, the same boiling point, the same ordinary physical properties. They differ only in their handedness in space — and the human nose tells them apart at once.
Where else you meet it
The R form is found in spearmint — Mentha spicata — and some related Mentha species. The S form is found in caraway seed, dill, and cumin.
For garden mint in Vietnam one has to be more cautious. The reference work Những cây thuốc và vị thuốc Việt Nam reports carvone at fifty to sixty per cent, but other sources give a different species and a different dominant compound. The garden mint entry explains why that name does not correspond to a single species.
Carvone also forms when limonene oxidises over time, so it appears as a trace in old citrus peel — aged tangerine peel is an example.
Dictionary entries that mention this compound
About the boiling-point figure
The boiling point is the same for both optical isomers — it is a physical property, and mirror images are identical in every ordinary physical property. Only smell and a chiral column can separate them. Why this detail matters