Material guide · 158
Material guide: longifolene — a pure compound with five unusable fields
· 15 min read
CAS 475-20-7, 16 suppliers, C15H24. It is a single compound, so its refractive index, specific gravity and optical rotation should each be a constant plus a little room. In practice the refractive index reads 1.42000 to 1.60000, thirty times the database's median width; the specific gravity reads 0.93000 to 1.11000; the optical rotation reads +14 to +54, forty degrees wide. All three have round endpoints. The melting point field says 156.20 °C while the appearance field calls it a liquid, and that temperature sits above its own boiling point of 150 to 151 °C at 36 mmHg. The assay field reads 95.00 to 100.00, the database's default template. Meanwhile its own structural isomer (−)-isolongifolene has 11 suppliers and a specification thirty times tighter. It appears zero times in 954 formulas. But it is a real material: a sesquiterpene from turpentine, given a full RIFM safety assessment in 2019, and in 2025 engineered into fungi to attract and kill mosquitoes.
About a 4 minute read.
The short version
- Name: longifolene, CAS 475-20-7, C15H24, molecular weight 204.36, 16 suppliers
- Odour type woody; odour: sweet, woody, rose, medicinal, fir needle
- Medium strength (rank 2), substantivity 24 hours, vapour pressure 0.031 mmHg
- It is a single compound, and five of its fields are unusable at once
- It appears zero times in 954 formulas
- But it is a real material: a sesquiterpene from turpentine, with a full RIFM assessment in 2019
Five fields
I have just swept the database for specification range widths, and this is the most extreme record it turned up. In order:
| Field | Registered value | Problem |
|---|---|---|
| Refractive index | 1.42000 to 1.60000 |
Width 0.18 against a database median of 0.0060: thirty times, with round endpoints |
| Specific gravity | 0.93000 to 1.11000 |
Width 0.18 against a median of 0.0080, also round endpoints |
| Optical rotation | +14.00 to +54.00 |
Forty degrees wide; the median is ten |
| Melting point | 156.20 °C. @ 0.00 mm Hg |
It is a liquid (appearance field), and this sits above its own boiling point at 36 mmHg |
| Assay | 95.00 to 100.00 |
The database's default template value |
A pure compound's refractive index should be one number. The interval 1.42 to 1.60 contains the true value, and it also contains half of organic chemistry.
The melting point is the best of them, because it trips two checks I have built at once:
- A liquid cannot melt above 50 °C, and the appearance field says "colorless to yellow clear oily liquid"
- 156.2 °C is above the boiling point field's 150–151 °C at 36 mmHg. A solid that melts at 156 °C cannot boil at 150 °C
And @ 0.00 mm Hg is meaningless as a pressure annotation. Melting points barely depend on pressure,
and 0 mmHg is a vacuum.
Its own isomer has a spec thirty times tighter
The sesquiterpenes sharing its molecular formula:
| Material | Suppliers | Refractive index | Width | Specific gravity |
|---|---|---|---|---|
| beta-caryophyllene | 61 | 1.498 – 1.504 | 0.006 | 0.899 – 0.908 |
| valencene | 44 | 1.498 – 1.510 | 0.012 | 0.910 – 0.922 |
| alpha-cedrene | 19 | 1.500 – 1.503 | 0.003 | 0.926 – 0.937 |
| alpha-humulene | 16 | 1.499 – 1.505 | 0.006 | 0.889 – 0.895 |
| (−)-isolongifolene | 11 | 1.495 – 1.501 | 0.006 | 0.926 – 0.932 |
| longifolene | 16 | 1.420 – 1.600 | 0.180 | 0.930 – 1.110 |
(−)-Isolongifolene is its structural isomer, has five fewer suppliers, and carries a specification thirty times tighter.
Every well-behaved sesquiterpene's refractive index sits between 1.495 and 1.510. Longifolene's true value is almost certainly there too, and its specific gravity's lower bound of 0.930 lines up with alpha-cedrene's 0.926–0.937.
The usable information exists. It is just not in this record's own fields; it is in its neighbours'.
What it actually is
Set the fields aside and this is a material with a history.
It is a sesquiterpene from pine turpentine, and Indian turpentine in particular is rich in it.
The occurrence field lists a long set of natural sources:
| Source | Content |
|---|---|
| Carrot seed oil | 1.24% |
| Hinoki leaf oil | 0.72% |
| Hinoki root oil | 0.64% |
| Lebanon cedarwood oil | 0.50% |
| Star anise, artichoke, corn root, cypress, geranium… | not quantified |
Widely distributed, nowhere abundant. That explains a material with a name, a CAS number and a RIFM assessment but only 16 suppliers: it is a constituent of other people's oils rather than something people buy.
Its odour field reads sweet, woody, rose, medicinal, fir needle. That fir needle is consistent with turning up in cedar and hinoki.
Zero appearances in the corpus
Across 954 formulas, longifolene appears zero times. So does isolongifolene.
For contrast, beta-caryophyllene from the same group does appear, and so does alpha-cedrene.
It is a material that has been recorded but not used.
(I tested the hypothesis that unpopular records go unchecked last round, and it failed: the correlation between supplier count and spec width is only −0.055. So I cannot say its fields are bad because nobody uses it. Alpha-humulene also has 16 suppliers and a perfectly normal spec.)
But research has kept using it
- In 2019, RIFM published a full fragrance ingredient safety assessment for it (PMID 31542430). A 16-supplier material receiving the same treatment as mainstream ones
- In 2025, its biosynthetic pathway was engineered into Metarhizium fungi so the fungus itself produces longifolene to attract and kill mosquitoes (PMID 41136733, Nat Microbiol)
The second is worth dwelling on. A sesquiterpene almost nobody in perfumery uses turns out to be a mosquito attractant, and the approach puts the gene into a fungus that already infects insects, making the bait and the killer the same organism.
A material's standing in perfumery says nothing about its standing anywhere else.
What this doesn't establish
- I did not look up longifolene's correct refractive index or specific gravity. I showed only that it disagrees with its family and that its specs are not shaped like measurements.
- "The true value should be 1.495 to 1.510" is inferred from its neighbours, not looked up.
- I judged the melting point wrong on the basis of the appearance and boiling point fields.
If the appearance field is itself wrong, that argument collapses. It carries
(est). - Zero appearances is a result for these 954 formulas, not an industry usage rate.
- I read neither the RIFM assessment nor the mosquito paper in full. I cite their titles and the fact that they exist.
- The mosquito paper has nothing to do with perfumery. I included it to make one point: this material is taken seriously elsewhere, just not inside formulas.