Moleculium

CID 6212

CHCl3

Chloroform

  • C 1
  • H 1
  • Cl 3
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5 atoms, 4 single bonds, tetrahedral.
Ball-and-stick model of chloroform: 1 carbon atom, 1 hydrogen atom and 3 chlorine atoms, 4 single bonds, tetrahedral. Carbon is grey, hydrogen white, chlorine green.
IUPAC name
chloroform
Molar mass
119.369(32) g/mol
Atoms
5
Shape
tetrahedral
SMILES
C(Cl)(Cl)Cl
InChIKey
HEDRZPFGACZZDS-UHFFFAOYSA-N
PubChem CID
6212

Made of

C , Carbon, nonmetal H , Hydrogen, nonmetal Cl , Chlorine, halogen
Structural formula of chloroform. 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 chloroform, drawn flat from PubChem's 2D record: 1 carbon atom, 1 hydrogen atom and 3 chlorine atoms, 4 single bonds. Each unlabelled corner is a carbon atom, and the one hydrogen on carbon is not drawn. Symbols carry their usual colours: chlorine green. A structural formula shows how the atoms are joined, not the shape of the molecule.

Replacing three of the four hydrogen atoms round the carbon of methane with chlorine gives chloroform, a member of the chloromethanes and a one-carbon halogenated hydrocarbon. It is a volatile liquid with an ether-like odour, in the words of the NCI Thesaurus, the US National Cancer Institute’s reference vocabulary. Once an inhaled anaesthetic, it is now used mainly in industry, as a solvent and to make a refrigerant, the NCI Thesaurus adds. It is also heavy, highly refractive, bending light strongly, sweet-tasting and not combustible, according to the Hazardous Substances Data Bank (HSDB).

Pure chloroform is light sensitive and decomposes in sunlight when air is absent, and in the dark when air is present. Reagent grades usually carry a little ethanol as a stabiliser. Heated until it decomposes, it gives off phosgene, a toxic gas.

Structure and bonding

Chloroform’s five atoms are joined by four single bonds: one carbon at the centre, with three chlorines and one hydrogen around it. In the Ball-and-stick view those four partners sit at the corners of a tetrahedron. Only one dichloromethane, CH2Cl2, exists, so the four positions round the carbon must be equivalent, which requires a tetrahedron, according to Chem1.

The tetrahedron here is slightly uneven. The model’s computed geometry places 110.6° between two chlorines and 108.3° between a chlorine and the hydrogen, with C–Cl bonds of 1.772 Å against 1.093 Å for C–H. The Stick view shows three long spokes and one short one. The Space-filling view wraps the carbon in three large chlorine spheres with the hydrogen a small cap on one face.

Bond dipoles can add up or cancel according to a molecule’s geometry, and chloroform has a dipole moment of 3.84 × 10−30 C·m, according to HSDB. The viewer draws no dipole, only atoms and bonds. The lone C–H bond also matters in the body. Chloroform carrying deuterium, a heavier isotope of hydrogen, in place of that hydrogen was less toxic and less readily metabolised, suggesting breaking C–H limits the rate of liver damage.

Where it turns up

Chloroform forms naturally, mostly in wet places: tropical oceans, forest soil, rice fields, swamps and peat moorlands, according to ATSDR, the US Agency for Toxic Substances and Disease Registry. Dry grasslands, volcanic eruptions and burning organic matter release it too.

Chlorine added to water makes small amounts of it, so treated drinking water, wastewater and swimming pools all carry traces. Landfills, hazardous waste sites and pulp and paper mills release it as well, according to the US Environmental Protection Agency (EPA). Exposure also comes with cigarette smoking, dry cleaning and plastic composites manufacturing, according to Haz-Map.

Chloroform breaks down slowly in air, so it may drift a long way, and because it dissolves in water it comes back down with rain. It clings poorly to soil, which lets it move through to groundwater. Chloroform is likely present almost everywhere, in ATSDR’s assessment.

Why it matters

Industry prepares chloroform on a massive scale by chlorinating methane or chloromethane, on HSDB’s account. Almost all of the United States’ output becomes HCFC-22, monochlorodifluoromethane, a refrigerant that also serves as raw material for polytetrafluoroethylene (PTFE), the plastic sold as Teflon. In 1981 that use took 96 per cent of production, according to HSDB. EPA’s Chemical Data Reporting puts the aggregated US product volume for 2023 at between 100 million and 250 million pounds. Smaller amounts serve as a solvent for fats, oils, rubber, waxes and resins, and as an extractant for pharmaceutical products.

Inhaled chloroform anaesthesia arrived in 1847, and Sir James Simpson’s discovery of its anaesthetic action ranks, for HSDB, among that century’s therapeutic triumphs. Queen Victoria asked for it at the birth of Prince Leopold. Until the century ended it was the most popular general anaesthetic for obstetrics, the care of women in childbirth, and for surgery, according to HSDB. Its flaw showed in 1899: in poorly ventilated operating rooms lit by flames, heat broke it down into toxic phosgene.

Properties

Properties of chloroform Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 6212.
Property Value Unit Source
Molecular formula (Hill order) CHCl3
Molar mass 119.369(32)   g/mol g/mol IUPAC/CIAAW 2024
Carbon atoms 1
Hydrogen atoms 1
Chlorine atoms 3
Bonds 4
PubChem molecular weight 119.37   g/mol g/mol PubChem

Safety

Chloroform is toxic if inhaled and harmful if swallowed, and under EU classification it carries the signal word Danger. It irritates skin and eyes, is suspected of causing cancer and of harming an unborn child, and damages organs through prolonged or repeated exposure. Its vapour is heavier than air and can collect in low spaces, crowding out oxygen. The PubChem Laboratory Chemical Safety Summary and the NIOSH Pocket Guide card for chloroform are the reference sheets for anyone who handles it.

Questions

What shape is a chloroform molecule?

Tetrahedral around its one carbon atom. ChEBI describes it as methane with three of its hydrogens replaced by chlorines, and the model draws exactly that: three C–Cl single bonds and one C–H single bond. Every chloromethane is tetrahedral on Chem1's account, with all four positions round the carbon equivalent. The computed conformer puts 110.6° between two chlorines and 108.3° between a chlorine and the hydrogen, calculated values rather than measured ones.

Why is chloroform no longer used as an anaesthetic?

Safer alternatives became available, according to ATSDR, the US Agency for Toxic Substances and Disease Registry. Its toxic properties ended its significance as an inhaled anaesthetic, on the account of the Hazardous Substances Data Bank (HSDB). It was banned in the United States over suspected carcinogenicity, according to MeSH, the US National Library of Medicine's subject vocabulary. All drug products containing it are on the US Food and Drug Administration's list of withdrawn products.

Does chloroform sink or float in water?

It sinks. The liquid has a density of 1.484 at 20 °C relative to water, and on CAMEO Chemicals' account it sinks because it is denser than water and only slightly soluble. Its solubility is 0.8 g per 100 mL at 20 °C according to the International Chemical Safety Cards, and one millilitre dissolves in about 200 mL of water at 25 °C according to HSDB. With alcohol, ether, benzene and oils it mixes in any proportion.

Is there chloroform in tap water and swimming pools?

In small amounts, yes, wherever the water has been chlorinated. It forms when drinking water, wastewater and swimming pools are chlorinated, according to the US Environmental Protection Agency. Showering, bathing and washing dishes in such water bring people into contact with it, according to ATSDR, the US Agency for Toxic Substances and Disease Registry. Exposure for the general population is still expected to be very low, and chloroform does not stay in the body long.

Made of the same elements

Same shape (tetrahedral)

Appears in these articles

Sources

  1. PubChem CID 6212, chloroform
  2. IUPAC/CIAAW, Abridged Standard Atomic Weights 2024
  3. PubChem Laboratory Chemical Safety Summary for chloroform (CID 6212)
  4. NIOSH Pocket Guide to Chemical Hazards, Chloroform
  5. ATSDR ToxFAQs, Chloroform
  6. Stephen Lower, Chem1 General Chemistry, §9.4 Polar Covalence (LibreTexts, CC BY 3.0)
  7. Stephen Lower, Chem1 General Chemistry, §9.5 Molecular Geometry (LibreTexts, CC BY 3.0)