# Phenanthrene

**Phenanthrene** is a polycyclic aromatic hydrocarbon (PAH) consisting of three fused benzene rings joined in an angular arrangement, with molecular formula C\(_{14}\)H\(_{10}\) and molecular weight 178.23 g/mol<sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/995)</sup>. It is a [structural isomer](https://www.edgepedia.org/structural-isomer) of anthracene, in which the same three rings are fused linearly, and its name combines the terms "phenyl" and "anthracene"<sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/995)</sup>. The compound occurs in coal tar, is produced by incomplete combustion of organic material, and serves mainly as a chemical intermediate<sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/995)</sup><sup> • </sup><sup>[2](https://gost.tpsgc-pwgsc.gc.ca/Contfs.aspx?ID=43&lang=eng)</sup>.

| Key fact | Detail |
|---|---|
| Identity | C\(_{14}\)H\(_{10}\), molecular weight 178.23 g/mol, CAS Registry Number 85-01-8<sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/995)</sup><sup> • </sup><sup>[3](https://webbook.nist.gov/cgi/cbook.cgi?ID=C85018&Mask=4)</sup> |
| Structure | Three fused benzene rings in an angular arrangement; isomer of linearly fused anthracene<sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/995)</sup><sup> • </sup><sup>[4](https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modules_(Organic_Chemistry)/Arenes/Properties_of_Arenes/Polycyclic_Aromatics)</sup> |
| Phase behavior | Melting point about 372 K (99 °C); boiling point about 609 K; solid at room temperature with very low volatility<sup>[3](https://webbook.nist.gov/cgi/cbook.cgi?ID=C85018&Mask=4)</sup><sup> • </sup><sup>[2](https://gost.tpsgc-pwgsc.gc.ca/Contfs.aspx?ID=43&lang=eng)</sup> |
| Water solubility | About 1 mg/L, very low<sup>[2](https://gost.tpsgc-pwgsc.gc.ca/Contfs.aspx?ID=43&lang=eng)</sup> |
| Sorption | log K\(_{oc}\) 3.8 to 6.0 depending on soil or sediment characteristics, indicating strong adsorption to organic matter<sup>[2](https://gost.tpsgc-pwgsc.gc.ca/Contfs.aspx?ID=43&lang=eng)</sup> |
| Carcinogen classification | IARC Group 3, not classifiable as to its carcinogenicity to humans<sup>[5](https://monographs.iarc.who.int/%20agents-classified-by-the-iarc)</sup> |
| Uses | Manufacture of dyestuffs, explosives, drugs, and phenanthrenequinone; biochemical research reagent<sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/995)</sup> |
| US production | 371,175 lb reported for 2023 under EPA Chemical Data Reporting<sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/995)</sup> |

## Structure and aromaticity

Phenanthrene contains three benzene rings fused at an angle, a topology called angular fusion or annulation, in contrast to the linear fusion of its isomer anthracene<sup>[4](https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modules_(Organic_Chemistry)/Arenes/Properties_of_Arenes/Polycyclic_Aromatics)</sup>. The molecule has 14 \(\pi\) electrons, satisfying the aromatic 4n + 2 rule with n = 3, and its resonance energy is listed at 381 kJ/mol against 347 kJ/mol for anthracene<sup>[6](https://www.chem.ucalgary.ca/courses/353/Carey5th/Ch11/ch11-5.html)</sup>.

**Why the angular isomer is more stable.** Phenanthrene has five Kekulé resonance structures (alternative bonding arrangements contributing to a molecule's stability), one more than anthracene, and this extra resonance makes it about 6 kcal per mol more stable<sup>[4](https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modules_(Organic_Chemistry)/Arenes/Properties_of_Arenes/Polycyclic_Aromatics)</sup>. Clar's aromatic \(\pi\)-sextet model, which assigns the dominant resonance structure to the form with the largest number of disjoint aromatic sextets, gives phenanthrene two \(\pi\)-sextets in its outer rings while anthracene has only one migrating sextet, a difference that accounts for phenanthrene's larger stability<sup>[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC6255896/)</sup>. The two bay-region hydrogen atoms in phenanthrene also participate in H−H bonding interactions proposed to contribute to its stability relative to anthracene<sup>[8](https://pubs.acs.org/doi/pdf/10.1021/jo061637p)</sup>.

## Physical properties

Phenanthrene appears as colorless monoclinic crystals with a faint aromatic odor, and its solutions exhibit blue fluorescence<sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/995)</sup>. The NIST Chemistry WebBook lists a melting temperature averaging 372 ± 2 K from 32 of 35 reported values, a triple point of 372.38 K, and a critical temperature of about 869 K<sup>[3](https://webbook.nist.gov/cgi/cbook.cgi?ID=C85018&Mask=4)</sup>. Reported boiling points cluster between 601 and 613 K<sup>[3](https://webbook.nist.gov/cgi/cbook.cgi?ID=C85018&Mask=4)</sup>. The enthalpy of vaporization is about 78.7 kJ/mol and the [enthalpy of sublimation](https://www.edgepedia.org/enthalpy-of-sublimation) averages 91 ± 3 kJ/mol<sup>[3](https://webbook.nist.gov/cgi/cbook.cgi?ID=C85018&Mask=4)</sup>. [Relative density](https://www.edgepedia.org/relative-density) is 1.18 g/cm\(^{3}\), so the solid sinks in water<sup>[2](https://gost.tpsgc-pwgsc.gc.ca/Contfs.aspx?ID=43&lang=eng)</sup>.

Under pressure the solid changes structure: x-ray diffraction identifies phase I with space group P2\(_{1}\) at 0 to 2.2 GPa, phase II with P2/m at 2.2 to 5.6 GPa, and phase III with P2/m plus Pmmm at 5.6 to 11.4 GPa; above 20.0 GPa the Raman spectrum indicates transformation into amorphous hydrogenated carbon<sup>[9](https://arxiv.org/abs/1303.1572)</sup>.

## Occurrence and production

Phenanthrene, along with anthracene, occurs in the anthracene oil (green oil) fraction of coal tar, and it is produced by fractional distillation of high-boiling coal-tar oil<sup>[10](https://www.msuniv.ac.in/images/distance%20education/learning%20materials/ug%20pg/ug/bsc_chemistry/III%20Year%20-%20DJY3A%20-%20Organic%20Chemistry%20II.pdf)</sup><sup> • </sup><sup>[11](https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=900P0100.TXT)</sup>. It is also formed by incomplete combustion of organic materials, including side-stream cigarette smoke, gasoline engine exhaust, and charcoal-broiled steaks, and it has been detected in used motor oil, crude oils, diesel exhaust, and creosote<sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/995)</sup>. More than 100 PAHs are known, generally occurring as complex mixtures in combustion by-products such as soot, and phenanthrene is more likely to be encountered mixed with other PAHs in coal tar, coal tar pitch, creosote, bitumen, and asphalt than as a pure substance<sup>[2](https://gost.tpsgc-pwgsc.gc.ca/Contfs.aspx?ID=43&lang=eng)</sup>.

A rare natural occurrence exists as the mineral ravatite, approved by the International Mineralogical Association in 1992 (IMA 1992-019), which is essentially phenanthrene, C\(_{14}\)H\(_{10}\), from Ravat, Tadzhikistan<sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/995)</sup>.

## Uses

Phenanthrene is used to make dyestuffs, explosives, drugs, and phenanthrenequinone, and as a reagent in biochemical research<sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/995)</sup>. It forms the basis for production of 9,10-phenanthrenequinone and 2,2'-diphenic acid<sup>[12](https://pubchem.ncbi.nlm.nih.gov/compound/85-01-8)</sup>. Oxidation with chromic acid in glacial acetic acid gives 9,10-phenanthrenequinone, the point of first attack being the 9,10 positions<sup>[13](https://www.collectionscanada.gc.ca/obj/s4/f2/dsk1/tape3/PQDD_0020/MQ48505.pdf)</sup>. US aggregated production volumes reported under EPA Chemical Data Reporting were 575,334 lb in 2020, 568,032 lb in 2021, 323,858 lb in 2022, and 371,175 lb in 2023<sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/995)</sup>.

## Environmental behavior

At 20 °C phenanthrene is a solid with very low volatility and very low solubility in water, about 1 mg/L<sup>[2](https://gost.tpsgc-pwgsc.gc.ca/Contfs.aspx?ID=43&lang=eng)</sup>. It adsorbs strongly to organic matter, with log K\(_{oc}\) values of 3.8 to 6.0 depending on soil or sediment characteristics, and a [Henry's law](https://www.edgepedia.org/henrys-law) constant of about 4 × 10\(^{-5}\) atm·m\(^{3}\)/mol gives moderate volatilization once dissolved<sup>[2](https://gost.tpsgc-pwgsc.gc.ca/Contfs.aspx?ID=43&lang=eng)</sup>. In soil it solubilizes very slowly, and once a source is removed, adsorbed phenanthrene persists for a long time, being released slowly in gaseous or dissolved forms<sup>[2](https://gost.tpsgc-pwgsc.gc.ca/Contfs.aspx?ID=43&lang=eng)</sup>.

**Degradation pathways.** Vapor-phase phenanthrene is degraded in the atmosphere by reaction with hydroxyl radicals and night-time nitrate radicals, with estimated half-lives of 14 and 6.4 hours respectively<sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/995)</sup>. It absorbs strongly at wavelengths above 290 nm and is expected to be susceptible to direct photolysis by sunlight<sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/995)</sup>; in surface fresh water under mid-summer sunlight at 40°N latitude its photolysis half-life is 8 hours, compared with 61 hours for naphthalene and 0.54 hours for benzo(a)pyrene<sup>[14](https://semspub.epa.gov/work/HQ/174390.pdf)</sup>. Biodegradation can also be significant: in the Japanese MITI test with activated sludge inoculum, phenanthrene at 100 mg/L reached 78.9% of its theoretical biochemical oxygen demand in 4 weeks, classifying it as readily biodegradable<sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/995)</sup>. A soil half-life of 26 days was measured at a low application rate of 2.1 µg/g incubated at 15 to 25 °C<sup>[1](https://pubchem.ncbi.nlm.nih.gov/compound/995)</sup>.

## Toxicology

The International Agency for Research on Cancer classifies phenanthrene in Group 3, not classifiable as to its carcinogenicity to humans<sup>[5](https://monographs.iarc.who.int/%20agents-classified-by-the-iarc)</sup>. The EPA's Integrated Risk Information System characterizes its cancer weight of evidence as Group D, not classifiable, based on no human data and inadequate animal data from a single gavage study in rats and several skin application and injection studies in mice<sup>[15](https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100VSOQ.TXT)</sup>. In mouse skin painting tests, phenanthrene's 1,2-, 3,4-, and 9,10-dihydrodiol metabolites failed to initiate tumors, and among 100 mice given phenanthrene over 9 months, none developed tumors.<sup>[12](https://pubchem.ncbi.nlm.nih.gov/compound/85-01-8)</sup> The Canada contaminant fact sheet notes that the compound is toxic and should be handled with care<sup>[2](https://gost.tpsgc-pwgsc.gc.ca/Contfs.aspx?ID=43&lang=eng)</sup>.

## References

1. [Phenanthrene, CID 995, PubChem](https://pubchem.ncbi.nlm.nih.gov/compound/995)
2. [Fact sheet: Phenanthrene, Guidance and Orientation for the Selection of Technologies, Public Services and Procurement Canada](https://gost.tpsgc-pwgsc.gc.ca/Contfs.aspx?ID=43&lang=eng)
3. [Phenanthrene, NIST Chemistry WebBook, SRD 69](https://webbook.nist.gov/cgi/cbook.cgi?ID=C85018&Mask=4)
4. [Polycyclic Aromatics, Chemistry LibreTexts](https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modules_(Organic_Chemistry)/Arenes/Properties_of_Arenes/Polycyclic_Aromatics)
5. [Agents Classified by the IARC Monographs, Volumes 1–142](https://monographs.iarc.who.int/%20agents-classified-by-the-iarc)
6. [Ch 11: Polyaromatics, University of Calgary course notes](https://www.chem.ucalgary.ca/courses/353/Carey5th/Ch11/ch11-5.html)
7. [Aromaticity Determines the Relative Stability of Kinked vs. Straight Topologies in Polycyclic Aromatic Hydrocarbons, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC6255896/)
8. [Polycyclic Benzenoids: Why Kinked is More Stable than Straight, Journal of Organic Chemistry](https://pubs.acs.org/doi/pdf/10.1021/jo061637p)
9. [Structural and vibrational properties of phenanthrene under pressure, arXiv](https://arxiv.org/abs/1303.1572)
10. [Organic Chemistry II course material, Manonmaniam Sundaranar University](https://www.msuniv.ac.in/images/distance%20education/learning%20materials/ug%20pg/ug/bsc_chemistry/III%20Year%20-%20DJY3A%20-%20Organic%20Chemistry%20II.pdf)
11. [Proposed Sediment Quality Criteria for the Protection of Benthic Organisms: Phenanthrene, US EPA](https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=900P0100.TXT)
12. [Phenanthrene, CID 85-01-8 record, PubChem](https://pubchem.ncbi.nlm.nih.gov/compound/85-01-8)
13. [Chemistry of Dihydrophenanthrene Ketal and its Application, Library and Archives Canada](https://www.collectionscanada.gc.ca/obj/s4/f2/dsk1/tape3/PQDD_0020/MQ48505.pdf)
14. [Technical Resource Document on Monitored Natural Recovery, EPA-600-R-14-083](https://semspub.epa.gov/work/HQ/174390.pdf)
15. [Provisional Peer-Reviewed Toxicity Values for Phenanthrene (CASRN 85-01-8), US EPA](https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100VSOQ.TXT)

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*Topic: Encyclopedia › Physical world and mathematics › Chemistry › Organic substances › Hydrocarbons and aromatic systems › Polycyclic aromatic hydrocarbons*

*Initially written Sep 17, 2026 · Reviewed: Oct 15, 2026 · Edited: Oct 15, 2026 · Last review: Oct 15, 2026*

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License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license