CID 931
C10H8
Naphthalene
- C 10
- H 8
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- IUPAC name
- naphthalene
- Molar mass
- 128.174(22) g/mol
- Atoms
- 18
- SMILES
- C1=CC=C2C=CC=CC2=C1
- InChIKey
- UFWIBTONFRDIAS-UHFFFAOYSA-N
- PubChem CID
- 931
Left at room temperature, solid naphthalene passes straight into vapour without melting first, a change called sublimation, far below its melting point of 80.2 °C. The white crystals smell strongly of mothballs, and the product reaches buyers as scales, powder, balls or cakes. NIOSH, the US National Institute for Occupational Safety and Health, lists tar camphor and white tar among its other names.
The US National Cancer Institute’s thesaurus classes it as a polycyclic hydrocarbon: a compound of carbon and hydrogen alone, built on more than one ring. Its formula is C10H8 and its molar mass 128.17 g/mol. The solid is denser than water and barely dissolves in it: HSDB, the Hazardous Substances Data Bank, gives 31 mg per litre at 25 °C. One gram, by contrast, dissolves in 3.5 mL of benzene or toluene, and ether takes it up readily.
Structure and bonding
The model sets ten carbon atoms in two hexagons that share one edge, with eight hydrogens around the rim. Each carbon on the shared edge bonds to three carbons and holds no hydrogen. Turned edge-on, the model thins to a line, all eighteen atoms in one plane. Space-filling swells them into a flat slab with two rounded lobes, Stick keeps only the bonds, and Labels marks every atom C or H.
Ball-and-stick, the opening view, draws the eleven carbon–carbon bonds as five doubles and six singles in alternation, the shared bond among the singles. That pattern is only one drawing. HSDB calls naphthalene a resonance hybrid, a molecule whose real bonding blends several such drawings. ChEBI (Chemical Entities of Biological Interest) describes it as two fused rings of benzene.
The model’s own bond lengths ignore the drawn orders. At one carbon a drawn double and a drawn single both measure 1.404 Å, and every other carbon–carbon bond falls between 1.392 and 1.404 Å. The shared bond, drawn single, is the model’s longest at 1.415 Å.
Where it turns up
In homes it has served as a moth repellent, set in closed drawers, closets and other storage spaces. HSDB also records it in attics to repel squirrels and bats, and around gardens and the edges of buildings against snakes and rabbits. One product, Enoz Old Fashioned Moth Balls, gives its active ingredient as naphthalene at 99.95 per cent. Its use as a moth repellent and insecticide has been falling with the arrival of chlorinated compounds such as p-dichlorobenzene.
Beyond the house, incomplete burning releases it, from fossil fuels and forest fires to cigarettes, and jet and diesel fuel contain it. Haz-Map counts it among the major components of creosote, which impregnates timber, and places the highest workplace levels where creosote-treated timber is made. Living plants produce it as well: ChEBI records it in the essential oils of many species, magnolia among them.
Why it matters
Coal tar is its main raw material. In the high-temperature tar from coke ovens it averages about 10 per cent, by quantity the most important compound there on HSDB’s account. It crystallises from the carbolic oil, the middle-boiling fraction, or cut, collected as the tar is distilled. Oils left over from pyrolysis, the breaking-up of hydrocarbons by heat, and petroleum fractions rich in ring compounds supply more. The product is sold by its freezing point, because that temperature tracks how much naphthalene a batch contains.
Its main use, the US Environmental Protection Agency (EPA) says, is making phthalic anhydride, though o-xylene is replacing it as the preferred raw material. In HSDB’s 1985 breakdown, phthalic anhydride took 60 per cent of the naphthalene used and exports 15 per cent. A tenth went to 1-naphthol, tetralin and a carbamate insecticide, 8 per cent to tanning agents and 7 per cent to surfactants, surface-active agents, and other uses. Until about 1963 imports met 10 to 20 per cent of US demand, a share that then fell below 5 per cent and stayed there.
Properties
| Property | Value | Unit | Source |
|---|---|---|---|
| Molecular formula (Hill order) | C10H8 | ||
| Molar mass | 128.174(22) g/mol | g/mol | IUPAC/CIAAW 2024 |
| Carbon atoms | 10 | ||
| Hydrogen atoms | 8 | ||
| Bonds | 19 | ||
| Single bonds | 14 | ||
| Double bonds | 5 | ||
| PubChem molecular weight | 128.17 g/mol | g/mol | PubChem |
Safety
Naphthalene is harmful if swallowed, suspected of causing cancer and very toxic to aquatic life under the EU’s harmonised classification. The EPA links short-term exposure, by breathing, swallowing or skin contact, to haemolytic anaemia, a shortage of red blood cells caused by their breakdown, and to nerve damage. The solid burns, though it can be hard to ignite. NIOSH’s naphthalene card, which also carries the workplace exposure limits, and the PubChem Laboratory Chemical Safety Summary are the sheets to consult.
Questions
How many rings does naphthalene have?
Two. ChEBI, the Chemical Entities of Biological Interest database, classes naphthalene as an ortho-fused bicyclic arene: an aromatic hydrocarbon whose two rings share one bond. Sharing that bond means sharing its two carbons, so two six-carbon rings hold ten carbons, not twelve. Those two carbons bond only to other carbons, which leaves eight hydrogens where two separate benzene molecules, C6H6 each, carry twelve. The result is C10H8.
Can naphthalene cause cataracts?
It can, through what the body makes of it. HSDB, the Hazardous Substances Data Bank, names the metabolite naphthalene dihydrodiol, not naphthalene itself, as the agent behind the cataracts. In rats it is made in the liver and reaches the lens, and the lens enzyme aldose reductase forms it too; blocking that enzyme prevents the cataracts. In a 1956 study 8 of 21 workers melting the solid in open vats had cataracts, and none were reported once procedures changed.
Is naphthalene more dangerous for some people?
Yes: infants, and people short of one enzyme. The EPA reports haemolytic anaemia, a shortage of red blood cells caused by their breakdown, in babies born to mothers who sniffed and swallowed mothballs while pregnant. Baby oil raises how much naphthalene an infant's skin takes up, HSDB records. Haz-Map, citing the American Conference of Governmental Industrial Hygienists, adds that workers who lack the enzyme glucose-6-phosphate dehydrogenase run a greater risk of that breakdown.
Does naphthalene cause cancer?
It carries several cancer classifications. The EPA places it in Group C, a possible human carcinogen, and finds the human data inadequate to show that it causes cancer in people. The US National Cancer Institute's thesaurus calls it reasonably anticipated to be a human carcinogen. The California Safe Cosmetics Program records that the International Agency for Research on Cancer places it in Group 2B, and the EU classification reads suspected of causing cancer.
Made of the same elements
- C8H8 Styrene 16 atoms, 16 bonds.
- C7H8 Toluene 15 atoms, 15 bonds.
- C6H6 Benzene 12 atoms, 12 bonds.
- C3H8 Propane 11 atoms, 10 single bonds.
- C4H6 1,3-Butadiene 10 atoms, 9 bonds.
- C4H10 Butane 14 atoms, 13 single bonds.
- C6H12 Cyclohexane 18 atoms, 18 single bonds.
- C4H10 Isobutane 14 atoms, 13 single bonds.
All 18 compounds made of carbon and hydrogen
- C10H16 Limonene 26 atoms, 26 bonds.
- C5H12 Pentane 17 atoms, 16 single bonds.
- C3H6 Propylene 9 atoms, 8 bonds.
- C2H6 Ethane 8 atoms, 7 single bonds.
- C6H14 Hexane 20 atoms, 19 single bonds.
- C2H4 Ethylene 6 atoms, 5 bonds.
- C8H18 Isooctane 26 atoms, 25 single bonds.
- C8H18 Octane 26 atoms, 25 single bonds.
- CH4 Methane 5 atoms, 4 single bonds, tetrahedral.
- C2H2 Acetylene 4 atoms, 3 bonds.