Benzaldehyde

Ball-and-stick Stick Space-filling

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14 atoms, 14 bonds.

IUPAC name: benzaldehyde
Molar mass: 106.124(16) g/mol
Atoms: 14
SMILES: C1=CC=C(C=C1)C=O
InChIKey: HUMNYLRZRPPJDN-UHFFFAOYSA-N
PubChem CID: 240

Made of

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

A bitter-almond odour marks benzaldehyde, a clear liquid that ranges from colourless to yellow. ChEBI, the Chemical Entities of Biological Interest database, defines it as a benzene ring bearing one formyl group, –CHO, and calls it the simplest aromatic aldehyde. It is also the parent of a whole class, the benzaldehydes. The formula C₆H₅CHO reads that way too: a benzene ring short of one hydrogen, then the formyl group.

Seven carbon atoms, six of hydrogen and one of oxygen give it a molar mass of 106.12 g/mol. Its name under the rules of the International Union of Pure and Applied Chemistry (IUPAC) is benzaldehyde as well. It is denser than water and poorly soluble in it, so the liquid sinks rather than floats. It mixes freely with alcohol, with ether and with oils.

Structure and bonding

The viewer builds benzaldehyde from 14 atoms and 14 bonds. Six carbons form a hexagon; five of them carry one hydrogen each, and the sixth holds the formyl carbon, which bears the last hydrogen and a double-bonded oxygen. Turned edge-on, the model thins to a line: all 14 atoms share one plane. In Space-filling the atoms merge into a flat slab with the oxygen at the tip of a short tail. Stick strips the frame to rods, and Labels marks every atom C, H or O.

Ball-and-stick fixes the ring’s bonds in one pattern, double and single taking turns round the hexagon. In PubChem’s computed model every ring bond measures 1.395 Å, shorter than the 1.454 Å single bond linking the ring to the formyl carbon. The C=O double bond measures 1.234 Å.

Atoms joined by more than one bond sit closer than singly bonded ones, Chem1 notes, so ring bonds shorter than that single bond are more than single. Part of the ring’s bonding electrons, the “second half” of its double bonds, is shared round the whole ring, as in benzene, rather than fixed in three double bonds.

Where it turns up

Bottles of almond extract contain benzaldehyde whether the label reads pure or imitation; both hold it in a water-based solution, on the account of the Hazardous Substances Data Bank (HSDB). It also goes by the names synthetic bitter almond oil and artificial almond oil. Its flavour profile from FEMA, the Flavor and Extract Manufacturers Association, adds cherry, burnt sugar, malt and roasted pepper to bitter almond. Plants make it as a metabolite, and it is recorded as a component of cinnamon.

Harvester ants and millipedes release it in their defensive excretions. In several noctuid moths it is a major male pheromone, a chemical signal to others of the same species. It forms part of the alarm pheromone of Trigona stingless bees and sets off alarm behaviour in honey bees. It also works as a repellent that keeps honey bees away during the honey harvest, according to HSDB.

Why it matters

Most of the world’s synthetic benzaldehyde comes from the air oxidation of toluene, on HSDB’s account. Its liquid-phase version, now dominant, came in the late 1950s from the Dow Chemical Company, within its route from toluene to phenol, and from Snia Viscosa. The other main route, hydrolysis of benzal chloride, a reaction with water, can leave detectable traces of chlorine compounds. The Food Chemicals Codex (FCC) food grade is defined as chlorine-free.

HSDB names its largest single use as making benzyl alcohol by hydrogenation, the addition of hydrogen. Benzaldehyde also goes into aniline dyes, perfumes, flavourings and medicines, dissolves resins and oils, and serves cosmetics as a fragrance. In 1965, on HSDB’s figures, 45 per cent went to odorants and flavourings, 30 per cent to dye intermediates and 25 per cent to other chemicals.

Because it inhibits enzymes, benzaldehyde has served in studies of enzyme kinetics, the rates at which enzyme reactions run. It was once registered as an insecticide but is no longer registered by the US Environmental Protection Agency (EPA) for any pesticide product.

Properties

Properties of benzaldehyde Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 240.
Property	Value	Unit	Source
Molecular formula (Hill order)	C₇H₆O
Molar mass	106.124(16) g/mol	g/mol	IUPAC/CIAAW 2024
Carbon atoms	7
Hydrogen atoms	6
Oxygen atoms	1
Bonds	14
Single bonds	10
Double bonds	4
PubChem molecular weight	106.12 g/mol	g/mol	PubChem

Safety

Pure benzaldehyde is harmful if swallowed under the EU’s harmonised classification. Some company notifications to the European Chemicals Agency add serious eye irritation, harm when inhaled, and drowsiness or dizziness. It is also a combustible liquid, and California’s cosmetics programme lists it as a fragrance allergen. The PubChem Laboratory Chemical Safety Summary gathers these classifications, along with the workplace exposure limits that apply to it.

Questions

Is benzaldehyde a flat molecule?

In PubChem's computed model, a calculation rather than a measurement, it is: none of its 14 atoms sits more than 0.0006 Å away from one plane. The six angles inside the ring all come to 120.0°. Around the formyl carbon the angles are 123.1° between oxygen and ring, 120.2° between oxygen and hydrogen and 116.7° between ring and hydrogen, and the CHO group lies in the ring's plane instead of twisting out of it.

Is benzaldehyde safe to eat?

As a flavouring, it is approved. The US Food and Drug Administration lists it as a flavouring agent, and it sits among the synthetic flavourings that are generally recognised as safe. An expert committee of the United Nations food and health agencies found no safety concern at current intakes. The pure liquid is classed as harmful if swallowed, and the PubChem Laboratory Chemical Safety Summary covers that hazard.

What happens to benzaldehyde in the body?

It enters through the skin and the lungs, spreads to the organs with a rich blood supply and does not build up in any one tissue, according to the Hazardous Substances Data Bank. Two molybdenum-containing enzymes, aldehyde oxidase and xanthine oxidase, turn it into benzoic acid. The skin itself makes that change quickly.

Does benzaldehyde oxidise easily?

Yes. Oxygen in the air converts it readily to benzoic acid, the same acid the body makes from it. The Hazardous Substances Data Bank calls it a strong reducing agent, a substance that gives electrons to another and is oxidised itself. In the laboratory it reduces ammoniacal silver nitrate, silver nitrate dissolved in ammonia, but not Fehling's solution.

Made of the same elements

C₆H₅COOH Benzoic acid 15 atoms, 15 bonds.
C₆H₅OH Phenol 13 atoms, 13 bonds.
C₇H₆O₃ Salicylic acid 16 atoms, 16 bonds.
C₃H₆O Acetone 10 atoms, 9 bonds.
C₄H₈O Butanone 13 atoms, 12 bonds.
CH₃OCH₃ Dimethyl ether 9 atoms, 8 single bonds.
C₂H₅OH Ethanol 9 atoms, 8 single bonds.
C₈H₈O₃ Methyl salicylate 19 atoms, 19 bonds.

All 51 compounds made of carbon, hydrogen and oxygen

C₂H₅COOH Propionic acid 11 atoms, 10 bonds.
C₈H₈O₃ Vanillin 19 atoms, 19 bonds.
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.
C₉H₈O₄ Aspirin 21 atoms, 21 bonds.
C₂H₅OC₂H₅ Diethyl ether 15 atoms, 14 single bonds.
C₂H₄O Ethylene oxide 7 atoms, 7 single bonds.
C₄H₆O₅ Malic acid 15 atoms, 14 bonds.
C₃H₈O₂ Propylene glycol 13 atoms, 12 single 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.
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.