Ethanol

Ball-and-stick Stick Space-filling

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9 atoms, 8 single bonds.

IUPAC name: ethanol
Molar mass: 46.0690(62) g/mol
Atoms: 9
SMILES: CCO
InChIKey: LFQSCWFLJHTTHZ-UHFFFAOYSA-N
PubChem CID: 702

Made of

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

Wine, beer and distilled spirits owe their alcohol to one compound, ethanol, which some species of yeast make from sugar. OpenStax defines an alcohol as a hydrocarbon in which an −OH group has taken the place of a hydrogen atom. In ethanol that group hangs from a chain of two carbon atoms, which gives C₂H₅OH and a molar mass of 46.07 g/mol. Every atom is carbon, hydrogen or oxygen, and every bond between them is single.

At room temperature it is a clear liquid with a weak, wine-like smell. The NIOSH pocket guide, from the US National Institute for Occupational Safety and Health, also lists it as grain alcohol and cologne spirit. OpenStax places it among the earliest organic compounds that people set out to make on purpose.

Structure and bonding

The model holds nine atoms joined by eight single bonds, each drawn as it really is. With Labels on, symbols mark two carbons, one oxygen and six hydrogens: three on the end carbon, two on the middle one and one on the oxygen. No one shape word fits the whole molecule. OpenStax explains that a chain of interior atoms has a local geometry at each atom instead.

In Ball-and-stick, each carbon sits at the centre of four bonds spread tetrahedrally. The oxygen’s two bonds meet at an angle, the bent arrangement OpenStax gives an −OH oxygen. Its two lone pairs, the other two of its four electron regions, are not drawn. PubChem’s computed 3D model, the one the viewer draws, puts C–C–O at 109.0° and C–O–H at 107.6°, calculated values rather than measured ones.

The Stick view thins the atoms away, leaving the bond lines and their angles. Space-filling swells each atom to its full size, and the chain becomes one compact body with the hydrogen of the −OH group at the oxygen end. That hydrogen is the only one not bonded to carbon, and it is the one that gives ethanol its hydrogen bonding.

Where it turns up

Figures for 2003 from the Hazardous Substances Data Bank (HSDB), in PubChem, send 92 per cent of fermentation ethanol to fuel and only 4 per cent to drinks. In cider vinegar the sugar of the juice becomes ethanol first and then acetic acid. A spilled glass of wine shows the molecule at work on a kitchen paper towel. The wine creeps upward because the cellulose fibres of the towel carry −OH groups that attract water and ethanol molecules strongly, and those molecules also attract one another.

Away from the glass, ethanol goes into hairsprays, mouthwashes and hand disinfectants. Denatured alcohol carries added substances that make it unfit to drink. Anhydrous denatured ethanol, blended with 70 to 80 per cent petrol by volume, runs internal combustion engines, and HSDB lists it as an octane booster in petrol. Burned completely, one mole of the liquid gives off 1366.8 kJ of heat.

Why it matters

Three compounds of nearly equal molar mass show what an O–H bond does. On OpenStax’s figures, propane (44 g/mol) boils at −42.1 °C and dimethyl ether (46 g/mol) at −24.8 °C, while ethanol boils at about 78 °C. Their shapes and masses are close, so their dispersion forces are similar. Dimethyl ether adds dipole–dipole attractions, but only ethanol carries an −OH group, and so only ethanol forms hydrogen bonds between its molecules.

Yeast makes ethanol for a reason of its own. Without oxygen, a cell has to turn NADH, the loaded form of the electron carrier NAD⁺, back into NAD⁺, or glycolysis, the sugar-splitting pathway, stalls. Yeast does it by reducing acetaldehyde, adding hydrogen, to make ethanol. The product also sets a ceiling: depending on strain and conditions, yeast tolerates from about 5 to 21 per cent ethanol.

In 2003 industrial ethanol went 60 per cent to solvents and 40 per cent to chemical intermediates, HSDB reports. One of those intermediates is ethyl acetate, an ester: the kind of compound an acid, here acetic acid, forms with an alcohol.

Properties

Properties of ethanol Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 702.
Property	Value	Unit	Source
Molecular formula (Hill order)	C₂H₆O
Molar mass	46.0690(62) g/mol	g/mol	IUPAC/CIAAW 2024
Carbon atoms	2
Hydrogen atoms	6
Oxygen atoms	1
Bonds	8
PubChem molecular weight	46.07 g/mol	g/mol	PubChem

Safety

Pure ethanol is a highly flammable liquid whose vapour is heavier than air, and it can burn with an invisible flame. European Chemicals Agency (ECHA) notifications carry the signal word Danger, and 37.7% of the company reports behind them add serious eye irritation. IARC, the International Agency for Research on Cancer, lists drinking alcoholic beverages as a known human carcinogen. Handling guidance is in the PubChem Laboratory Chemical Safety Summary and the NIOSH card for ethyl alcohol.

Questions

What is denatured alcohol?

It is ethanol with added substances, called denaturants, that generally make it unfit to drink without limiting its other uses. HSDB says the usual denaturant for industrial ethanol is crude pyridine, at 0.5 to 1 per cent by weight. It is sometimes also coloured with a trace of methyl violet so that it is easy to recognise.

Is ethanol a base because it has an OH group?

No. In sodium hydroxide and potassium hydroxide the OH exists as separate OH⁻ ions held in an ionic compound, and that free ion is what makes them bases. In ethanol the −OH is fastened to carbon by a covalent bond, so OpenStax notes that alcohols do not behave like those bases.

How is ethanol made?

One route is fermentation, in which yeasts turn sugars into ethanol; HSDB adds biomass such as agricultural wastes, and cellulose broken down by enzymes, as feedstocks. The other is the hydration of ethylene, which OpenStax says yields large quantities. Industrial ethanol for solvents and fuel runs to 96.5 per cent by volume, while the absolute grade reaches 99.7 to 99.8 per cent.

Does ethanol mix with water?

Yes, in any proportion: HSDB lists it as miscible with water at 25 °C. The mixture behaves oddly, though. One volume of ethanol stirred into one volume of water gives only 1.92 volumes, not two. Water and ethanol also form an azeotrope, a mixture that boils without changing composition, at 95 per cent ethanol by weight.

Made of the same elements

CH₃OCH₃ Dimethyl ether 9 atoms, 8 single bonds.
C₃H₆O Acetone 10 atoms, 9 bonds.
C₂H₆O₂ Ethylene glycol 10 atoms, 9 single bonds.
CH₃CHO Acetaldehyde 7 atoms, 6 bonds.
C₂H₄O Ethylene oxide 7 atoms, 7 single bonds.
C₂H₅COOH Propionic acid 11 atoms, 10 bonds.
C₃H₇OH 1-Propanol 12 atoms, 11 single bonds.
CH₃COOH Acetic acid 8 atoms, 7 bonds.

All 51 compounds made of carbon, hydrogen and oxygen

C₃H₈O Isopropyl alcohol 12 atoms, 11 single bonds.
C₃H₆O₃ Lactic acid 12 atoms, 11 bonds.
CH₃OH Methanol 6 atoms, 5 single bonds.
C₄H₈O Butanone 13 atoms, 12 bonds.
C₂H₄O₃ Glycolic acid 9 atoms, 8 bonds.
C₆H₅OH Phenol 13 atoms, 13 bonds.
C₃H₈O₂ Propylene glycol 13 atoms, 12 single bonds.
C₆H₅CHO Benzaldehyde 14 atoms, 14 bonds.
C₃H₇COOH Butyric acid 14 atoms, 13 bonds.
CH₃COOC₂H₅ Ethyl acetate 14 atoms, 13 bonds.
CH₂O Formaldehyde 4 atoms, 3 bonds.
C₃H₈O₃ Glycerol 14 atoms, 13 single bonds.
C₄H₉OH 1-Butanol 15 atoms, 14 single bonds.
C₆H₅COOH Benzoic acid 15 atoms, 15 bonds.
C₂H₅OC₂H₅ Diethyl ether 15 atoms, 14 single bonds.
HCOOH Formic acid 5 atoms, 4 bonds.
C₄H₆O₅ Malic acid 15 atoms, 14 bonds.
H₂CO₃ Carbonic acid 6 atoms, 5 bonds.
H₂C₂O₄ Oxalic acid 8 atoms, 7 bonds.
C₇H₆O₃ Salicylic acid 16 atoms, 16 bonds.
C₄H₆O₆ Tartaric acid 16 atoms, 15 bonds.
C₈H₈O₃ Methyl salicylate 19 atoms, 19 bonds.
C₈H₈O₃ Vanillin 19 atoms, 19 bonds.
C₆H₈O₆ Ascorbic acid 20 atoms, 20 bonds.
C₉H₈O₄ Aspirin 21 atoms, 21 bonds.
C₆H₈O₇ Citric acid 21 atoms, 20 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.