CID 996

C₆H₅OH

Phenol

Ball-and-stick Stick Space-filling

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13 atoms, 13 bonds.

IUPAC name: phenol
Molar mass: 94.113(14) g/mol
Atoms: 13
SMILES: C1=CC=C(C=C1)O
InChIKey: ISWSIDIOOBJBQZ-UHFFFAOYSA-N
PubChem CID: 996

Made of

Structural formula of phenol. Each unlabelled corner is a carbon atom, and the five hydrogens on carbon are not drawn. It shows which atoms are joined to which, not the shape. The model above shows the shape.

Phenol is also called carbolic acid, a synonym NIOSH, the US National Institute for Occupational Safety and Health, lists on its card, and it is indeed a weak acid. ChEBI, a database of biological chemicals, describes it as benzene bearing one hydroxy group, OH, and the parent of all phenols. Six carbon atoms, six hydrogen atoms and one oxygen atom give it a molar mass of 94.11 g/mol.

The benzene ring draws electrons away from the OH group, Chem1 explains, more weakly than a carboxyl group does, so its hydrogen can leave as in an acid. The acid constant, K_a, is 1.1 × 10⁻¹⁰, against 1.8 × 10⁻⁵ for acetic acid: a very weak acid.

The Hazardous Substances Data Bank (HSDB) describes translucent, needle-shaped crystals that draw water from the air and turn pink or red when impure. They melt at about 41 °C, and mixing in about 8 per cent water turns them liquid.

Structure and bonding

The viewer holds 13 atoms and 13 bonds: a hexagon of six carbons, five capped by a hydrogen and the sixth bonded to an oxygen that carries the last hydrogen. Seen edge-on, all 13 atoms lie in one plane, the hydrogen on oxygen included. The oxygen’s two bonds, one to the ring carbon and one to its hydrogen, meet at an angle, not in a straight line. Labels picks out the single O among the C and H symbols.

In both Ball-and-stick and Stick, double and single bonds take turns around the hexagon, three of each: a single Kekulé form. In the real ring these bonding electrons, called π electrons, are not fixed in three bonds. Chem1 describes them as delocalised, spread in rings of electron density on each face of the flat ring. The model’s measurements agree: every ring bond is 1.395 Å, drawn single or double alike, and the C–O bond is 1.361 Å.

Space-filling merges everything into a flat, rounded slab with a small knob at the oxygen. The drawing is the neutral molecule; in water a small share can lose the hydrogen on oxygen, leaving the phenolate ion that ChEBI names as its conjugate base.

Where it turns up

ATSDR, the Agency for Toxic Substances and Disease Registry, says phenol is made in factories and also occurs naturally. Small amounts turn up in some foods: fried chicken, mountain cheese, smoked summer sausage and certain fish. Smoking, or breathing someone else’s smoke, is another everyday source of exposure.

Inside the body it appears as a breakdown product. ChEBI lists it as a human xenobiotic metabolite, formed from substances foreign to the body. The NORMAN network of environmental laboratories names it as a known human metabolite of benzene.

On the pharmacy shelf it goes into throat lozenges and mouthwashes, and the US Environmental Protection Agency (EPA) lists ear and nose drops too. After a small, single release, ATSDR says it generally leaves soil within about two to five days but can stay in water for a week or more. Larger or repeated releases last much longer, and fish, other animals and plants do not accumulate it.

Why it matters

In the United States most phenol is made by oxidising cumene, with acetone forming as a by-product; HSDB names toluene oxidation as the only other route of industrial importance. The EPA puts US production in 2023 at between 2.5 and 4 billion pounds.

The EPA names phenolic resins as the primary use, serving the plywood, construction, car and appliance industries, and ATSDR adds nylon and other synthetic fibres. In HSDB’s 1985 breakdown, phenolic resins took 45 per cent and bisphenol A, a building block of polycarbonate plastic, 20 per cent.

Those resins began in 1907–1909, when the Belgian chemist Leo Baekeland developed Bakelite, the first commercial synthetic moulding plastic in Chem1’s account. Because each phenol ring offers several reactive sites, its resin with formaldehyde forms cross-links at each of them, as Chem1 describes. Bakelite was prized for insulating electricity in light fittings, sockets and other wiring parts. Phenolic adhesives still bond plywood, and the resins go into paints and varnishes.

Properties

Properties of phenol Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 996.
Property	Value	Unit	Source
Molecular formula (Hill order)	C₆H₆O
Molar mass	94.113(14) g/mol	g/mol	IUPAC/CIAAW 2024
Carbon atoms	6
Hydrogen atoms	6
Oxygen atoms	1
Bonds	13
Single bonds	10
Double bonds	3
PubChem molecular weight	94.11 g/mol	g/mol	PubChem

Safety

Concentrated phenol is toxic and corrosive, and its Globally Harmonized System (GHS) classification carries the signal word Danger. It is toxic if swallowed, inhaled or on the skin, causes severe burns and eye damage, is suspected of causing genetic defects and may damage organs through repeated exposure. Its anaesthetic action numbs the skin it whitens instead of causing burning pain, CAMEO Chemicals notes, and HSDB records that it passes through intact skin into the blood. The PubChem Laboratory Chemical Safety Summary for phenol and its NIOSH Pocket Guide card give the full hazard picture.

Questions

Is phenol an acid or an alcohol?

It has features of both. MeSH, the US medical subject vocabulary, calls it an aromatic alcohol, and ChEBI describes an OH group on a benzene ring. Yet that OH can give up its hydrogen, leaving the phenolate ion; it is also known as carbolic acid. It is a very weak acid: Chem1 gives K_a 1.1 × 10⁻¹⁰, against 1.8 × 10⁻⁵ for acetic acid.

Why does the phenol model show three double bonds in its ring?

The model's file fixes each bond as single or double, so the ring appears in one Kekulé form. In phenol's real ring, the carbons are held together by a framework of single σ (sigma) bonds, as Chem1 describes. Each carbon also has a p orbital pointing above and below the ring, and these merge into rings of electron density shared by all six carbons. That is why no ring bond is truly single or double.

Is phenol used in medicine?

Yes, in several roles. The World Health Organization's ATC drug classification lists it as a throat antiseptic, a local anaesthetic, a skin antiseptic and disinfectant, and a sclerosing agent, which is injected to shrink blood vessels. ATSDR, the US Agency for Toxic Substances and Disease Registry, adds that some people with chronic pain or spasticity receive phenol injections, and clinics use phenol-containing products for chemical peels that remove skin lesions.

What happens to phenol in the body?

The Hazardous Substances Data Bank (HSDB) says it is absorbed by every route, intact skin included. Most is joined directly to sulfate or glucuronide groups, according to HSDB. A smaller share is first oxidised on the ring, giving products that NORMAN lists as catechol and hydroquinone, which are joined the same way. The kidneys remove most of it in urine. In volunteers the half-life was about 3.5 hours, and ATSDR says raised urine phenol can point to recent exposure.

Made of the same elements

C₆H₅CHO Benzaldehyde 14 atoms, 14 bonds.
C₆H₅COOH Benzoic acid 15 atoms, 15 bonds.
C₃H₆O Acetone 10 atoms, 9 bonds.
C₇H₆O₃ Salicylic acid 16 atoms, 16 bonds.
C₄H₈O Butanone 13 atoms, 12 bonds.
CH₃OCH₃ Dimethyl ether 9 atoms, 8 single bonds.
C₂H₅OH Ethanol 9 atoms, 8 single bonds.
C₂H₅COOH Propionic acid 11 atoms, 10 bonds.

All 51 compounds made of carbon, hydrogen and oxygen

C₃H₇OH 1-Propanol 12 atoms, 11 single bonds.
C₃H₇COOH Butyric acid 14 atoms, 13 bonds.
CH₃COOC₂H₅ Ethyl acetate 14 atoms, 13 bonds.
C₂H₆O₂ Ethylene glycol 10 atoms, 9 single bonds.
C₃H₈O Isopropyl alcohol 12 atoms, 11 single bonds.
C₃H₆O₃ Lactic acid 12 atoms, 11 bonds.
C₄H₉OH 1-Butanol 15 atoms, 14 single bonds.
CH₃CHO Acetaldehyde 7 atoms, 6 bonds.
C₂H₅OC₂H₅ Diethyl ether 15 atoms, 14 single bonds.
C₂H₄O Ethylene oxide 7 atoms, 7 single bonds.
C₄H₆O₅ Malic acid 15 atoms, 14 bonds.
C₈H₈O₃ Methyl salicylate 19 atoms, 19 bonds.
C₃H₈O₂ Propylene glycol 13 atoms, 12 single bonds.
C₈H₈O₃ Vanillin 19 atoms, 19 bonds.
CH₃COOH Acetic acid 8 atoms, 7 bonds.
C₆H₈O₆ Ascorbic acid 20 atoms, 20 bonds.
C₃H₈O₃ Glycerol 14 atoms, 13 single bonds.
CH₃OH Methanol 6 atoms, 5 single bonds.
C₄H₆O₆ Tartaric acid 16 atoms, 15 bonds.
C₉H₈O₄ Aspirin 21 atoms, 21 bonds.
C₆H₈O₇ Citric acid 21 atoms, 20 bonds.
C₂H₄O₃ Glycolic acid 9 atoms, 8 bonds.
CH₂O Formaldehyde 4 atoms, 3 bonds.
HCOOH Formic acid 5 atoms, 4 bonds.
H₂CO₃ Carbonic acid 6 atoms, 5 bonds.
C₆H₁₂O₆ Fructose 24 atoms, 24 single bonds.
C₆H₁₂O₆ Glucose 24 atoms, 24 single bonds.
H₂C₂O₄ Oxalic acid 8 atoms, 7 bonds.
C₁₀H₂₀O Menthol 31 atoms, 31 single bonds.
C₁₄H₁₄O₃ Naproxen 31 atoms, 32 bonds.
C₁₅H₁₆O₂ Bisphenol A 33 atoms, 34 bonds.
C₁₃H₁₈O₂ Ibuprofen 33 atoms, 33 bonds.
C₂₀H₁₄O₄ Phenolphthalein 38 atoms, 41 bonds.
C₁₈H₂₄O₂ Estradiol 44 atoms, 47 bonds.
C₁₂H₂₂O₁₁ Lactose 45 atoms, 46 single bonds.
C₁₂H₂₂O₁₁ Sucrose 45 atoms, 46 single bonds.
C₁₉H₂₈O₂ Testosterone 49 atoms, 52 bonds.
C₁₆H₃₂O₂ Palmitic acid 50 atoms, 49 bonds.
C₂₁H₃₀O₂ Progesterone 53 atoms, 56 bonds.
C₁₈H₃₄O₂ Oleic acid 54 atoms, 53 bonds.
C₂₁H₃₀O₅ Cortisol 56 atoms, 59 bonds.
C₂₇H₄₄O Cholecalciferol 72 atoms, 74 bonds.
C₂₇H₄₆O Cholesterol 74 atoms, 77 bonds.