Isopropyl alcohol

Ball-and-stick Stick Space-filling

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12 atoms, 11 single bonds.

IUPAC name: propan-2-ol
Molar mass: 60.0960(86) g/mol
Atoms: 12
Polarity: polar
SMILES: CC(C)O
InChIKey: KFZMGEQAYNKOFK-UHFFFAOYSA-N
PubChem CID: 3776

Made of

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

Sold as a 70 per cent solution in water, rubbing alcohol is isopropyl alcohol, according to CAMEO Chemicals, a US emergency-response database quoted in PubChem. Its name from the International Union of Pure and Applied Chemistry (IUPAC), propan-2-ol, records the one detail that sets it apart. The chain has three carbon atoms, and the −OH group hangs from the second of them.

OpenStax treats any alcohol as a hydrocarbon with one hydrogen swapped for an −OH group. Here the rest of the molecule is hydrogen, plus a single oxygen atom, for a molar mass of 60.1 g/mol. The liquid is volatile and colourless, with a sharp, musty smell. The Hazardous Substances Data Bank (HSDB) compares that smell to a blend of ethanol and acetone. Among the other names in the pocket guide of NIOSH, the US occupational safety institute, are IPA and dimethyl carbinol.

Structure and bonding

Twelve atoms and eleven single bonds make up the model. With Labels on, the symbols show what the name promises: the O sits on the middle carbon, which also holds one H and both end carbons. Each end carbon carries three hydrogens, and the twelfth atom, a hydrogen, is bonded to the oxygen.

In Ball-and-stick the chain forks at its centre, a short Y with the oxygen as one arm. OpenStax reads a molecule with several inner atoms one atom at a time. By that method each carbon has four bonds spread tetrahedrally, and the oxygen, with two bonds and two lone pairs, is bent; the lone pairs are not drawn. The Stick view strips the atoms back to their bonds and leaves the branch point bare.

In Space-filling the two CH₃ groups crowd round the middle carbon. Each bond drawn is single, and that is the real bonding: OpenStax notes that an alcohol’s oxygen is held by single covalent bonds. HSDB gives a dipole moment of 1.69 debye for the gas, a measured separation of charge that makes it polar in OpenStax’s sense. In OpenStax’s account, O–H groups on neighbouring molecules attract strongly, a dipole–dipole attraction called hydrogen bonding.

Where it turns up

Rubbing alcohol is only the start. The CAMEO entry lists cosmetics, hair preparations, perfumes, soaps, window cleaners, lacquers and antifreezes. Haz-Map, a database of workplace hazards, records it as a disinfectant, a household solvent and a fuel antifreeze. It also names semiconductor manufacturing among the jobs where workers meet it.

Applied to the skin, it serves as an antiseptic, according to the Toxin and Toxin Target Database (T3DB). Laboratories use it to preserve pathological specimens and to draw water out of tissue samples.

Traces reach food as well. Inks that print on tablets, gum and sweets may contain it. The body makes a little too: T3DB says gut bacteria produce small amounts.

Why it matters

Where the −OH group sits decides what oxidation makes of it. OpenStax defines oxidation at a carbon as a C–H bond replaced by a C–O bond. An alcohol whose −OH carbon is bonded to two other carbons becomes a ketone, whose C=O carbon is bonded to two carbons, and propan-2-ol is that case. OpenStax names its oxidation as one commercial route to acetone, beside fermenting corn or molasses. In HSDB’s 1984 consumption breakdown, 24 per cent went to make acetone; other profiles in the same record put that share at 10 and 15 per cent.

With water it mixes in any proportion. OpenStax gives it as a general rule that polar solvents tend to dissolve polar substances better. The two also form an azeotrope, a mixture that boils without changing composition: 87.7 per cent isopropyl alcohol by mass, boiling at 80.37 °C.

The US Environmental Protection Agency’s 2023 reporting places national production between one and two and a half billion pounds. In 1993, HSDB says, chemical intermediates took 34 per cent and personal care and household products 24 per cent.

Properties

Properties of isopropyl alcohol Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 3776.
Property	Value	Unit	Source
Molecular formula (Hill order)	C₃H₈O
Molar mass	60.0960(86) g/mol	g/mol	IUPAC/CIAAW 2024
Carbon atoms	3
Hydrogen atoms	8
Oxygen atoms	1
Bonds	11
PubChem molecular weight	60.1 g/mol	g/mol	PubChem

Safety

Isopropyl alcohol is a highly flammable liquid that causes serious eye irritation and may cause drowsiness or dizziness. Companies report these three hazard statements to the European Chemicals Agency, and the flammability one carries the signal word Danger. Heavier than air, the vapour can spread along the ground and flash back to a flame, and repeated or prolonged contact can dry and crack the skin. The PubChem Laboratory Chemical Safety Summary and the NIOSH card are the sheets to consult.

Questions

Is isopropyl alcohol the same as rubbing alcohol?

Rubbing alcohol is isopropyl alcohol diluted with water. CAMEO Chemicals, a US emergency-response database quoted in PubChem, says it is sold as a 70 per cent solution in water. The Hazardous Substances Data Bank lists purer grades too: anhydrous, at least 99.8 per cent, and a cosmetic grade of 91 per cent by volume. All are the same compound, propan-2-ol.

What is the boiling point of isopropyl alcohol?

It boils at 82.3 °C at normal atmospheric pressure, according to the Hazardous Substances Data Bank. The same record gives its heat of vaporisation, the energy needed to turn one mole of liquid into vapour, as 45.39 kJ/mol at 25 °C. The International Chemical Safety Card puts the vapour's density at 2.1 times that of air, so the vapour collects low down.

Is isopropyl alcohol flammable?

Yes, highly. Almost every classification sent to the European Chemicals Agency calls it a highly flammable liquid and vapour, under the signal word Danger. HSDB gives a flash point of 12 °C, the temperature at which its vapour can catch light. NIOSH puts it in Class IB of flammable liquids. The PubChem safety summary covers storage and fire.

What is the difference between isopropyl alcohol and ethanol?

Both are alcohols, but ethanol, CH₃CH₂OH, has two carbons and its −OH group sits on the end one. Isopropyl alcohol has three carbons, with the −OH group on the middle one, which is why oxidation turns it into a ketone, acetone. HSDB describes its smell as something like a mixture of ethanol and acetone. It is not a drink: swallowed, it causes drunkenness and vomiting.

Made of the same elements

C₃H₇OH 1-Propanol 12 atoms, 11 single bonds.
C₄H₈O Butanone 13 atoms, 12 bonds.
C₃H₈O₂ Propylene glycol 13 atoms, 12 single bonds.
C₃H₆O Acetone 10 atoms, 9 bonds.
C₃H₇COOH Butyric acid 14 atoms, 13 bonds.
CH₃COOC₂H₅ Ethyl acetate 14 atoms, 13 bonds.
C₃H₈O₃ Glycerol 14 atoms, 13 single bonds.
C₄H₉OH 1-Butanol 15 atoms, 14 single bonds.

All 51 compounds made of carbon, hydrogen and oxygen

C₂H₅OC₂H₅ Diethyl ether 15 atoms, 14 single bonds.
CH₃OCH₃ Dimethyl ether 9 atoms, 8 single bonds.
C₂H₅OH Ethanol 9 atoms, 8 single bonds.
C₂H₅COOH Propionic acid 11 atoms, 10 bonds.
C₂H₆O₂ Ethylene glycol 10 atoms, 9 single bonds.
C₃H₆O₃ Lactic acid 12 atoms, 11 bonds.
CH₃CHO Acetaldehyde 7 atoms, 6 bonds.
C₂H₄O Ethylene oxide 7 atoms, 7 single bonds.
C₆H₅OH Phenol 13 atoms, 13 bonds.
CH₃COOH Acetic acid 8 atoms, 7 bonds.
C₆H₅CHO Benzaldehyde 14 atoms, 14 bonds.
CH₃OH Methanol 6 atoms, 5 single bonds.
C₆H₅COOH Benzoic acid 15 atoms, 15 bonds.
C₂H₄O₃ Glycolic acid 9 atoms, 8 bonds.
C₄H₆O₅ Malic acid 15 atoms, 14 bonds.
C₈H₈O₃ Methyl salicylate 19 atoms, 19 bonds.
C₈H₈O₃ Vanillin 19 atoms, 19 bonds.
C₆H₈O₆ Ascorbic acid 20 atoms, 20 bonds.
CH₂O Formaldehyde 4 atoms, 3 bonds.
C₇H₆O₃ Salicylic acid 16 atoms, 16 bonds.
C₄H₆O₆ Tartaric acid 16 atoms, 15 bonds.
C₉H₈O₄ Aspirin 21 atoms, 21 bonds.
C₆H₈O₇ Citric acid 21 atoms, 20 bonds.
HCOOH Formic acid 5 atoms, 4 bonds.
H₂CO₃ Carbonic acid 6 atoms, 5 bonds.
H₂C₂O₄ Oxalic acid 8 atoms, 7 bonds.
C₆H₁₂O₆ Fructose 24 atoms, 24 single bonds.
C₆H₁₂O₆ Glucose 24 atoms, 24 single 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.