CID 3672

C₁₃H₁₈O₂

Ibuprofen

C 13
H 18
O 2

Ball-and-stick Stick Space-filling

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33 atoms, 33 bonds.

IUPAC name: 2-[4-(2-methylpropyl)phenyl]propanoic acid
Molar mass: 206.285(32) g/mol
Atoms: 33
SMILES: CC(C)CC1=CC=C(C=C1)C(C)C(=O)O
InChIKey: HEFNNWSXXWATRW-UHFFFAOYSA-N
PubChem CID: 3672

Made of

C H O

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

A pharmacy painkiller, an arthritis prescription and a fever suspension for children can all rest on the same small molecule. Its core is a six-membered ring of carbon atoms with two arms at opposite corners. One arm is a branched hydrocarbon chain; the other ends in a carboxylic acid group, in which an oxygen atom holds a hydrogen atom. IUPAC, the body that standardises chemical names, calls it 2-[4-(2-methylpropyl)phenyl]propanoic acid.

The name reads from the acid end: a propanoic acid carrying a phenyl ring, and on that ring’s far corner a 2-methylpropyl group. Pure ibuprofen forms colourless, stable crystals. The Hazardous Substances Data Bank (HSDB), quoted on PubChem, gives a melting point of 75 to 77 °C. The solid barely dissolves in water but mixes readily into most organic solvents.

Structure and bonding

The model holds 33 atoms, thirteen carbon, eighteen hydrogen and two oxygen, linked by 33 bonds. In Ball-and-stick, the ring appears with three double and three single bonds taking turns. That drawing is one resonance form, one way of placing the bonds; OpenStax treats the real molecule as the average of all such forms. Its π electrons, the second bond of each double bond, are delocalised over all six carbons, and substituents leave that intact. The model’s own geometry agrees: its six ring bonds all measure between 1.386 and 1.395 Å.

Seen edge-on, the ring is a flat line, the branched chain leaving one corner and the acid group the opposite one. There, the carbon of the C=O double bond has three neighbours in one plane, the trigonal planar arrangement OpenStax gives a carbonyl carbon. Oxygen has far higher electronegativity, an atom’s pull on bonding electrons, so that C=O bond is polar.

Space-filling merges the atoms into one long outline of carbon and hydrogen, two red oxygen spheres at one tip. With Labels on, one H sits on an O: the acid hydrogen. The model shows the neutral acid, and a base removes that hydrogen to give a salt.

Where it turns up

Over the counter, ibuprofen is sold as a pain reliever. It comes as tablets and as liquid suspensions for children, sold under names such as Advil and Motrin. Prescriptions cover rheumatoid arthritis, osteoarthritis and psoriatic arthritis, over short courses and long ones. Vets use it as an anti-inflammatory as well. It also appears on the WHO Model List of Essential Medicines.

Industry makes it from isobutylbenzene. German prescriptions in 1995 came to an estimated 105 tons a year, and the drug made Denmark’s top ten medicines that year. Reports to the US Environmental Protection Agency put American volume between 50,000 and 250,000 pounds a year from 2020 to 2023. The Human Metabolome Database lists fat tissue, the kidney, the placenta and platelets among the tissues where ibuprofen or its metabolites occur.

Why it matters

Ibuprofen belongs to the nonsteroidal anti-inflammatory drugs, or NSAIDs, and eases pain, lowers fever and damps inflammation. DrugBank ties those effects to cyclooxygenase (COX), the enzyme that turns arachidonic acid into the precursors of prostaglandins, signalling molecules of pain and fever. Ibuprofen blocks both of its forms. Blocking COX-2 cuts the prostaglandins behind swelling and pain, while blocking COX-1 is thought to cause side effects such as stomach ulcers.

That is not the whole account. DrugBank itself calls the exact mechanism unknown and mentions reports linking pain relief to the body’s own cannabinoids. PubChem’s pharmacology notes add that other mechanisms may contribute to the anti-inflammatory effect.

The two mirror-image forms, R and S, also matter. PubChem’s record is the mixture of both, and the model is labelled as neither. In the body, 53 to 65 per cent of the R form converts to the S form, which DrugBank calls the more active one. The liver then works on the branched side chain, and the products leave in urine.

Properties

Properties of ibuprofen Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 3672.
Property	Value	Unit	Source
Molecular formula (Hill order)	C₁₃H₁₈O₂
Molar mass	206.285(32) g/mol	g/mol	IUPAC/CIAAW 2024
Carbon atoms	13
Hydrogen atoms	18
Oxygen atoms	2
Bonds	33
Single bonds	29
Double bonds	4
PubChem molecular weight	206.28 g/mol	g/mol	PubChem

Safety

Ibuprofen is a medicine, and as a pure substance it carries hazard classifications of its own. Every company that gave a classification in notifications to the European Chemicals Agency (ECHA) calls it harmful if swallowed. Most add eye and respiratory irritation, and a minority suspect harm to fertility or the unborn child. Japan’s official classification is stricter. Medicinal use follows the label and a pharmacist, and the substance itself is covered by the PubChem Laboratory Chemical Safety Summary.

Questions

What does the ibuprofen molecule look like?

At its centre is a flat hexagon of six carbons, with an arm on each of two opposite corners. One arm is a four-carbon branched chain, the 2-methylpropyl group; the other is a propanoic acid, ending in COOH. The 3D model counts 33 atoms. Its ring appears as alternating single and double bonds, but OpenStax treats the π electrons of such a ring, those forming the second bonds, as delocalised, spread over all six carbons.

Is ibuprofen an acid?

Yes, a weak one. It is a carboxylic acid, and OpenStax describes that family as only partly ionised in water. Its pKa, a measure of acid strength in which a lower value means a stronger acid, is given as 4.91 and 5.2 by HSDB and as 5.3 by DrugBank. A base removes the acid hydrogen to give an ionic salt, as OpenStax shows for every carboxylic acid.

Does ibuprofen dissolve in water?

Hardly at all. HSDB gives its solubility in water as 21 mg per litre at 25 °C, while it dissolves readily in most organic solvents and very well in alcohol. Its log K_ow is 3.97; K_ow is the ratio in which a substance divides between octanol, an oily solvent, and water, and a positive log value means octanol takes the larger share.

Is ibuprofen the same kind of drug as aspirin?

Both are nonsteroidal anti-inflammatory drugs, and OpenStax names them together when it warns that heavy use of such drugs can trigger stomach ulcers and gastritis. The WHO's drug classification places ibuprofen among the propionic acid derivatives. PubChem's pharmacology notes add that painkillers of this non-narcotic kind typically do not bind opioid receptors and are not addictive.

Made of the same elements

C₁₅H₁₆O₂ Bisphenol A 33 atoms, 34 bonds.
C₁₀H₂₀O Menthol 31 atoms, 31 single bonds.
C₁₄H₁₄O₃ Naproxen 31 atoms, 32 bonds.
C₁₈H₂₄O₂ Estradiol 44 atoms, 47 bonds.
C₂₀H₁₄O₄ Phenolphthalein 38 atoms, 41 bonds.
C₁₂H₂₂O₁₁ Lactose 45 atoms, 46 single bonds.
C₁₂H₂₂O₁₁ Sucrose 45 atoms, 46 single bonds.
C₉H₈O₄ Aspirin 21 atoms, 21 bonds.

All 51 compounds made of carbon, hydrogen and oxygen

C₈H₈O₃ Methyl salicylate 19 atoms, 19 bonds.
C₁₉H₂₈O₂ Testosterone 49 atoms, 52 bonds.
C₈H₈O₃ Vanillin 19 atoms, 19 bonds.
C₆H₁₂O₆ Fructose 24 atoms, 24 single bonds.
C₆H₁₂O₆ Glucose 24 atoms, 24 single bonds.
C₁₆H₃₂O₂ Palmitic acid 50 atoms, 49 bonds.
C₄H₉OH 1-Butanol 15 atoms, 14 single bonds.
C₆H₅COOH Benzoic acid 15 atoms, 15 bonds.
C₂H₅OC₂H₅ Diethyl ether 15 atoms, 14 single bonds.
C₆H₅CHO Benzaldehyde 14 atoms, 14 bonds.
C₃H₇COOH Butyric acid 14 atoms, 13 bonds.
CH₃COOC₂H₅ Ethyl acetate 14 atoms, 13 bonds.
C₇H₆O₃ Salicylic acid 16 atoms, 16 bonds.
C₄H₈O Butanone 13 atoms, 12 bonds.
C₆H₅OH Phenol 13 atoms, 13 bonds.
C₂₁H₃₀O₂ Progesterone 53 atoms, 56 bonds.
C₃H₈O₂ Propylene glycol 13 atoms, 12 single bonds.
C₃H₇OH 1-Propanol 12 atoms, 11 single bonds.
C₆H₈O₆ Ascorbic acid 20 atoms, 20 bonds.
C₃H₈O₃ Glycerol 14 atoms, 13 single bonds.
C₃H₈O Isopropyl alcohol 12 atoms, 11 single bonds.
C₁₈H₃₄O₂ Oleic acid 54 atoms, 53 bonds.
C₆H₈O₇ Citric acid 21 atoms, 20 bonds.
C₂H₅COOH Propionic acid 11 atoms, 10 bonds.
C₃H₆O Acetone 10 atoms, 9 bonds.
C₂₁H₃₀O₅ Cortisol 56 atoms, 59 bonds.
C₂H₆O₂ Ethylene glycol 10 atoms, 9 single bonds.
C₃H₆O₃ Lactic acid 12 atoms, 11 bonds.
CH₃OCH₃ Dimethyl ether 9 atoms, 8 single bonds.
C₂H₅OH Ethanol 9 atoms, 8 single bonds.
C₄H₆O₅ Malic acid 15 atoms, 14 bonds.
CH₃COOH Acetic acid 8 atoms, 7 bonds.
C₄H₆O₆ Tartaric acid 16 atoms, 15 bonds.
CH₃CHO Acetaldehyde 7 atoms, 6 bonds.
C₂H₄O Ethylene oxide 7 atoms, 7 single bonds.
C₂H₄O₃ Glycolic acid 9 atoms, 8 bonds.
CH₃OH Methanol 6 atoms, 5 single bonds.
HCOOH Formic acid 5 atoms, 4 bonds.
H₂CO₃ Carbonic acid 6 atoms, 5 bonds.
CH₂O Formaldehyde 4 atoms, 3 bonds.
H₂C₂O₄ Oxalic acid 8 atoms, 7 bonds.
C₂₇H₄₄O Cholecalciferol 72 atoms, 74 bonds.
C₂₇H₄₆O Cholesterol 74 atoms, 77 bonds.