Moleculium

CID 2519

C8H10N4O2

Caffeine

  • C 8
  • H 10
  • N 4
  • O 2
Viewer controls

Drag to rotate; pinch or Ctrl + scroll to zoom. Arrow keys rotate, + − zoom, R resets.

24 atoms, 25 bonds.
Ball-and-stick model of caffeine: 8 carbon atoms, 10 hydrogen atoms, 4 nitrogen atoms and 2 oxygen atoms, 25 bonds (21 single, 4 double). Carbon is grey, hydrogen white, nitrogen blue, oxygen red.
IUPAC name
1,3,7-trimethylpurine-2,6-dione
Molar mass
194.194(24) g/mol
Atoms
24
Polarity
polar
SMILES
CN1C=NC2=C1C(=O)N(C(=O)N2C)C
InChIKey
RYYVLZVUVIJVGH-UHFFFAOYSA-N
PubChem CID
2519

Made of

C , Carbon, nonmetal H , Hydrogen, nonmetal N , Nitrogen, nonmetal O , Oxygen, nonmetal
Structural formula of caffeine. 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. Structural formula of caffeine, drawn flat from PubChem's 2D record: 8 carbon atoms, 10 hydrogen atoms, 4 nitrogen atoms and 2 oxygen atoms, 25 bonds (21 single, 4 double). Each unlabelled corner is a carbon atom, and the one hydrogen on carbon is not drawn. Symbols carry their usual colours: nitrogen blue and oxygen red. A structural formula shows how the atoms are joined, not the shape of the molecule.

Stripped out of coffee or tea, caffeine is a heap of odourless white crystals with a bitter taste. They grow as hexagonal prisms or as long, flexible, silky strands. The US Food and Drug Administration (FDA) classes the compound as a methylxanthine. Its IUPAC name, 1,3,7-trimethylpurine-2,6-dione, reads as a parts list. It describes a purine framework of two fused rings, with methyl groups at positions 1, 3 and 7 and a carbon–oxygen double bond at 2 and 6.

Three close relatives each carry one methyl group fewer, and they are also what the body makes of it. About 80 per cent is metabolised to paraxanthine (1,7-dimethylxanthine), about 10 per cent to theobromine and 4 per cent to theophylline. OpenStax treats caffeine as a weak base, yet a 1 per cent solution in water has a pH of 6.9 and leaves litmus unchanged.

Structure and bonding

Fourteen heavy atoms, eight carbon, four nitrogen and two oxygen, make a six-membered ring fused to a five-membered one along a shared edge. With Labels on, all four nitrogens appear inside the rings, three of them carrying a methyl group. All ten hydrogen atoms sit on carbon: nine in those methyl groups, one on the smaller ring.

Ball-and-stick shows one Lewis structure with every bond fixed. Four bonds are double: two C=O on the larger ring, a C=N in the smaller ring and a C=C on the shared edge. OpenStax notes that where several such structures fit the same atoms, the real electron distribution is an average of them, so the drawing is one way of writing caffeine. Turned edge-on, the model shows all fourteen heavy atoms in one plane, as PubChem’s calculated geometry places them.

In the Space-filling view it becomes a flat plate with methyl groups bulging from its rim. OpenStax calls caffeine somewhat polar, with polar and nonpolar regions, which lets it dissolve in solvents of varying polarity. A hydrogen bond needs hydrogen on nitrogen, oxygen or fluorine, and none is drawn here, so caffeine molecules cannot hydrogen-bond to each other.

Where it turns up

Caffeine occurs naturally in coffee and cocoa beans, in tea and mate leaves, in kola nuts and in guarana, on the Merck Index’s list. Green coffee beans hold 0.9 to 2.6 per cent. HSDB, the Hazardous Substances Data Bank, reports only a small loss by sublimation in the roaster and about 85 per cent of the caffeine reaching the brew.

Commercial caffeine comes from tea dust, which holds up to 5 per cent, from the waste of decaffeinated coffee, or from synthesis.

Food takes 80 per cent of it and medicines 16, on HSDB’s split. Cosmetics use 3 per cent, adding it to condition skin and to calm redness or puffiness.

Why it matters

Caffeine stimulates the central nervous system, sharpening alertness and sometimes bringing restlessness and agitation. It spreads quickly through the tissues, crossing the placenta and the blood–brain barrier.

How caffeine acts is not fully settled. In HSDB’s account it competitively inhibits phosphodiesterase, the enzyme that breaks down cyclic AMP (adenosine monophosphate), and the extra cyclic AMP drives most of its effects. DrugBank calls the mechanism complex, treats that route as one probable account and ties the alertness to caffeine blocking the A2a receptor, one of four receptors for adenosine.

Blocking those receptors also strengthens the brain’s breathing response to carbon dioxide. Doctors use it for short-term treatment of apnoea of prematurity, pauses in breathing in premature babies, though DrugBank says the exact mechanism there is unknown. It narrows blood vessels, which helps headaches caused by widened vessels in the brain. The liver clears it mainly through the enzyme CYP1A2, so caffeine can interact with drugs that the same enzyme breaks down.

Properties

Properties of caffeine Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 2519.
Property Value Unit Source
Molecular formula (Hill order) C8H10N4O2
Molar mass 194.194(24)   g/mol g/mol IUPAC/CIAAW 2024
Carbon atoms 8
Hydrogen atoms 10
Nitrogen atoms 4
Oxygen atoms 2
Bonds 25
Single bonds 21
Double bonds 4
PubChem molecular weight 194.19   g/mol g/mol PubChem

Safety

Caffeine in cola and pure caffeine powder are labelled differently. The FDA lists it as “generally recognized as safe” in cola-type beverages. Most European Chemicals Agency (ECHA) notifications for pure caffeine give the signal word Warning, harmful if swallowed; Japan’s adds possible damage to fertility or the unborn child. The PubChem Laboratory Chemical Safety Summary for caffeine is the sheet to consult.

Questions

What does a caffeine molecule look like?

The model has 24 atoms joined by 25 bonds, built round two fused rings. Two oxygen atoms and the three methyl carbons lie in the same plane as the rings, while most of the methyl hydrogens stand out above and below it. That flatness comes from PubChem's calculated geometry, and the fixed single and double bonds are one Lewis drawing of the molecule.

Does caffeine dissolve in water?

Yes, and far better when the water is hot. HSDB gives one gram dissolving in 46 mL of water, in 5.5 mL at 80 °C and in only 1.5 mL at the boil. OpenStax explains the solubility by caffeine being a somewhat polar molecule in a polar liquid. Its mix of polar and nonpolar regions also lets it dissolve in dichloromethane and ethyl acetate.

How is coffee decaffeinated?

Supercritical carbon dioxide passed through steamed coffee beans removes 97 to 99 per cent of the caffeine and leaves the flavour and aroma compounds behind. Since carbon dioxide is a gas at ordinary conditions, it leaves the beans easily afterwards. Dichloromethane and ethyl acetate also extract it, but both are toxic, which raised concerns about solvent left in the coffee.

How long does caffeine stay in the body?

Its plasma half-life, the time for the level in the blood to fall by half, is 3 to 5 hours in adults on HSDB's figure; DrugBank gives about 5 hours. It lingers in pregnancy, 15 hours or more on DrugBank's figure, while in smokers the half-life can be up to 50 per cent shorter. Newborn babies clear it far more slowly than adults.

Made of the same elements

All 25 compounds made of carbon, hydrogen, nitrogen and oxygen

Sources

  1. PubChem CID 2519, caffeine
  2. IUPAC/CIAAW, Abridged Standard Atomic Weights 2024
  3. PubChem Laboratory Chemical Safety Summary for caffeine (CID 2519)
  4. OpenStax, Chemistry 2e, §7.4 Formal Charges and Resonance
  5. OpenStax, Chemistry 2e, §10.1 Intermolecular Forces
  6. OpenStax, Chemistry 2e, §10.4 Phase Diagrams
  7. OpenStax, Chemistry 2e, §14.3 Relative Strengths of Acids and Bases