How to Search for a Compound in the NIST Chemistry WebBook
You can search the NIST Chemistry WebBook by compound name, chemical formula, CAS registry number, molecular weight, chemical structure, or selected ion energetics and spectral properties. The search runs inside the Chemistry WebBook itself, which you reach by clicking the entry link on the welcome page at webbook.nist.gov. The site is part of the NIST Standard Reference Data Program and is free to use at present, though NIST states it reserves the right to charge for access in the future.
What you can search by
The welcome page lists the identifiers and properties the WebBook accepts for a compound lookup:
| Search route | Use it when |
|---|---|
| Name | You know a common or systematic compound name |
| Chemical formula | You know the formula but not the exact name |
| CAS registry number | You have the CAS number and want an unambiguous match |
| Molecular weight | You only know the mass and need to narrow candidates |
| Chemical structure | You can draw or specify the structure |
| Ion energetics and spectral properties | You are matching on ionization energy, appearance energy, electron affinity, proton affinity, gas basicity, or cluster ion binding energies, or on spectral features |
Because a name can be ambiguous, a CAS registry number or a drawn structure usually gives the cleanest match. Formula and molecular weight are useful when the name is uncertain but may return several isomers.
Step-by-step: run a search
- Go to webbook.nist.gov and open the Chemistry WebBook from the welcome page. The welcome page itself only introduces the database; the search tools live inside the WebBook.
- Choose the search type that matches what you know — name, formula, CAS registry number, molecular weight, structure, or ion energetics/spectral properties.
- Enter your value. For a name or formula, type it as given; for a structure, provide the structure in the form the search expects; for ion energetics or spectra, supply the property value or peak you are matching.
- Submit the search and review the results list. Confirm you have the right compound by checking the formula, CAS number, or structure shown for each hit.
- Open the compound record to see the data available for it.
Expected result: a compound record containing whichever of the WebBook's data types apply to that substance — for example thermochemical data (enthalpy of formation, enthalpy of combustion, heat capacity, entropy, phase transition enthalpies and temperatures, vapor pressure), reaction thermochemistry, IR, mass, UV/Vis, gas chromatography, electronic and vibrational spectra, diatomic molecular constants, ion energetics, or thermophysical properties for fluids.
What data you can expect to find
The scale of the database tells you how likely a search is to return something:
- Thermochemical data for over 7,000 organic and small inorganic compounds
- Reaction thermochemistry for over 8,000 reactions
- IR spectra for over 16,000 compounds
- Mass spectra for over 33,000 compounds
- UV/Vis spectra for over 1,600 compounds
- Gas chromatography data for over 27,000 compounds
- Electronic and vibrational spectra for over 5,000 compounds
- Constants of diatomic molecules for over 600 compounds
- Ion energetics data for over 16,000 compounds
- Thermophysical property data for 74 fluids
If a compound is not in these sets, no search route will produce a record for it.
Common sticking points
- Searching on the welcome page. The welcome page describes the WebBook but is not the search interface; you must enter the WebBook first.
- Ambiguous names. A name search can return multiple compounds. Cross-check the formula, CAS number, or structure before using the data.
- Assuming a property exists. Coverage differs by data type — a compound with mass spectra may have no thermochemical entry, and fluid thermophysical data covers only 74 fluids.
- Treating results as guaranteed. NIST states it uses its best efforts to deliver a high-quality, verified copy of the database but makes no warranties, and is not liable for damage from errors or omissions. Verify critical values against the primary sources cited in the record.
- Assuming permanent free access. The welcome page notes NIST reserves the right to charge for access in the future, so do not treat current access as guaranteed to remain free.