2-Butene
Athanor · official
C4H8 · 56.11 g/mol
IUPAC name: (E)-but-2-ene
Also called trans-2-butene, beta-butylene
DangerExtremely flammable gasNames and identifiers
- IUPAC name
- (E)-but-2-ene
- Synonyms
- trans-2-butene, beta-butylene, trans-2-Butene
+ 36 more
(E)-But-2-ene, trans-Butene, trans-but-2-ene, 2-BUTENE, (E)-, 2-trans-Butene, beta-trans-Butylene, Low-boiling butene-2, trans-1,2-Dimethylethylene, e-but-2-ene, 017NGL487F, CHEBI:48365, RefChem:933259, 210-855-3, 618-356-6, Pseudobutylene, beta-Butylene, (E)-2-Butene, Butene-2, Butylene-2, (2E)-but-2-ene, (2E)-2-Butene, CH3CH=CHCH3, MFCD00064458, Dimethylethylene, beta-Butene, .beta.-Butylene, Butene, 2-, 2-Butene-trans, CCRIS 8971, HSDB 180, EINECS 203-452-9, 2-Butene, (2E)-, BRN 1718755, UNII-017NGL487F, UNII-S1SK37516R, HSDB 5723
- Molecular formula
- C4H8
- Empirical formula
- CH2
- Molecular weight
- 56.11 g/mol
- Exact mass
- 56.06260
- CAS number
- 624-64-6
- PubChem CID
- 62695
- Canonical SMILES
- CC=CC
- Isomeric SMILES
- C/C=C/C
- InChI
- InChI=1S/C4H8/c1-3-4-2/h3-4H,1-2H3/b4-3+
- InChIKey
- IAQRGUVFOMOMEM-ONEGZZNKSA-N
- Molfile
Names, InChI and the identifiers from PubChem, retrieved 2026-10-14.
Physical properties
- Appearance
- 2-butene appears as a colorless liquefied petroleum gas. Asphyxiate gas. Flammability limits in air 1.8-9.7% by volume.[1]
3 values
From CAMEO Chemicals, the most authoritative source here.
Value As written Source –shown 2-butene appears as a colorless liquefied petroleum gas. Asphyxiate gas. Flammability limits in air 1.8-9.7% by volume. [1] CAMEO Chemicals – Gas Vapor; Liquid [2] EPA Chemical Data Reporting (CDR) – COLOURLESS COMPRESSED LIQUEFIED GAS. [3] ILO-WHO International Chemical Safety Cards (ICSCs) - Odor
- Slightly aromatic odor[4]
- Melting point
- -105.5 °C[3]
2 values
2 of 2 sources agree on it (most common value).
Value As written Source −105.5 °Cshown -105.5 °C [3] ILO-WHO International Chemical Safety Cards (ICSCs) −105.5 °C -105.5 °C [5] PAC Chemical Database, U.S. Department of Energy - Boiling point
- 0.9 °C[3]
2 values
2 of 2 sources agree on it (most common value).
Value As written Source 0.9 °Cshown 0.9 °C [3] ILO-WHO International Chemical Safety Cards (ICSCs) 0.8 °C 0.8 °C @760 [mm Hg] [5] PAC Chemical Database, U.S. Department of Energy - Density
- 0.6042 g/cu cm at 20/4 °C[4]
2 values
Only one source reports it.
Value As written Source 0.6042 g/mLshown 0.6042 g/cu cm at 20/4 °C [4] Hazardous Substances Data Bank (HSDB)cites Larranaga, M.D., Lewis, R.J. Sr., Lewis, R.A.; Hawley's Condensed Chemical Dictionary 16th Edition. John Wiley & Sons, Inc. Hoboken, NJ 2016., p. 217 – 0.599 @25 °C [5] PAC Chemical Database, U.S. Department of Energy 3 more values were reported but failed the checks (unreadable or out of range), so they are not shown.
- Solubility in water
- Solubility in water, mg/l at 25 °C: 511 (very slightly soluble)[3]
4 values
From ILO-WHO International Chemical Safety Cards (ICSCs), the most authoritative source here.
Value As written Source – Solubility in water, 511 mg/L at 25 °C [4] Hazardous Substances Data Bank (HSDB)cites Suzuki T; J Computer-Aided Molecular Design 5: 149-66 (1991) – Insoluble in water [4] Hazardous Substances Data Bank (HSDB)cites Larranaga, M.D., Lewis, R.J. Sr., Lewis, R.A.; Hawley's Condensed Chemical Dictionary 16th Edition. John Wiley & Sons, Inc. Hoboken, NJ 2016., p. 217 – Soluble in organic solvents [4] Hazardous Substances Data Bank (HSDB)cites Larranaga, M.D., Lewis, R.J. Sr., Lewis, R.A.; Hawley's Condensed Chemical Dictionary 16th Edition. John Wiley & Sons, Inc. Hoboken, NJ 2016., p. 217 –shown Solubility in water, mg/l at 25 °C: 511 (very slightly soluble) [3] ILO-WHO International Chemical Safety Cards (ICSCs) - log P
- 2.31[3]
3 values
2 of 2 sources agree on it (most common value).
Value As written Source – log Kow = 1.85 (mixture of 70% cis- and 30% trans-2-Butene) [4] Hazardous Substances Data Bank (HSDB)cites OECD SIDS. 2-Butene (107-10-7). Screening Information Data Set (SIDS) of OECD High Production Volume Chemicals Programme. Available from, as of Jan 2, 2018: https://hpvchemicals.oecd.org/UI/Search.aspx – log Kow = 2.31 [4] Hazardous Substances Data Bank (HSDB)cites Hansch, C., Leo, A., D. Hoekman. Exploring QSAR - Hydrophobic, Electronic, and Steric Constants. Washington, DC: American Chemical Society., 1995., p. 9 –shown 2.31 [3] ILO-WHO International Chemical Safety Cards (ICSCs) - Vapor pressure
- Vapor pressure = 1493 mmHg at 20 °C[4]
5 values
2 of 3 sources agree on it (most common value).
Value As written Source 1600 mmHg 1600 mm Hg at 25 °C /cis-2-Butene/ [4] Hazardous Substances Data Bank (HSDB)cites Daubert, T.E., R.P. Danner. Physical and Thermodynamic Properties of Pure Chemicals Data Compilation. Washington, D.C.: Taylor and Francis, 1989. 1493 mmHgshown Vapor pressure = 1493 mm Hg at 20 °C [4] Hazardous Substances Data Bank (HSDB)cites Geilen FMA et al; Butenes. Ullmann's Encyclopedia of Industrial Chemistry. 7th ed. (1999-2018). New York, NY: John Wiley & Sons. Online Posting Date: 31 Jan 2014. 1760 mmHg 1,760 mm Hg at 25 °C [4] Hazardous Substances Data Bank (HSDB)cites Daubert, T.E., R.P. Danner. Physical and Thermodynamic Properties of Pure Chemicals Data Compilation. Washington, D.C.: Taylor and Francis, 1989. 1500 mmHg Vapor pressure, kPa at 20 °C: 199 [3] ILO-WHO International Chemical Safety Cards (ICSCs) 1750 mmHg 1750 [mm Hg] @25 °C [5] PAC Chemical Database, U.S. Department of Energy - Flash point
- -19.99 °C (-3.98 °F) - closed cup[4]
- Autoignition temperature
- 324 °C[3]
2 values
2 of 2 sources agree on it (most common value).
Value As written Source 324 °C 324 °C (615 °F) [4] Hazardous Substances Data Bank (HSDB)cites National Fire Protection Association; Fire Protection Guide to Hazardous Materials. 14TH Edition, Quincy, MA 2010, p. 325-22 324 °Cshown 324 °C [3] ILO-WHO International Chemical Safety Cards (ICSCs) - Viscosity
- Reported, but no value passed the checks.
The value and why
- 0.00763 mPa (could not be read; source [4])
Each value as its source reports it, with the source's number after it (listed under References). Where several sources report a property, the row shows the value most of them agree on, the rule the app uses; open the values to see every one.
Calculated
- Heavy atoms
- 4
- Rings
- 0
- Aromatic rings
- 0
- Fraction sp³ carbons (Fsp3)
- 0.5
- H-bond donors
- 0
- H-bond acceptors
- 0
- Rotatable bonds
- 0
- TPSA (Ų)
- 0
- Formal charge
- 0
- XLogP3
- 2.3 PubChem
- Complexity
- 15 PubChem
- Stereocenters
- None
- Double-bond geometry
- C2=C3: E
- Point group
- C2h of one 3D conformer with its hydrogens, by Athanor’s engine (as in the app)
Elemental analysis
- C85.63%
- H14.37%
Isotope pattern
Each peak is a nominal mass with its abundance-weighted exact mass, as a percentage of the tallest, from IUPAC natural isotope abundances.
Computed from the structure with RDKit 2026.09 when this page was built, beside PubChem's own computed values from its record; where the two differ, both are shown.
Predicted
- log P
- 1.58 Crippen (Wildman and Crippen 1999)
- log S (water solubility)
- -1.18 ESOL (Delaney 2004), log mol/L
- Synthetic accessibility
- 3.12 SA score, 1 easy to 10 hard (Ertl and Schuffenhauer 2009)
Drug-likeness: Lipinski’s rule of five
- Molecular weight ≤ 500: 56.11
- log P ≤ 5 (Crippen): 1.58
- H-bond donors ≤ 5: 0
- H-bond acceptors ≤ 10: 0
Passes all four rules.
¹³C NMR shifts, predicted
Predictions, not measurements; each names its method. A measured log P, where a source reports one, is under Physical properties.
Safety
Danger
Harmonized EU classification (CLP Annex VI). Source [6].
- Flammable
- Compressed gas
- H220Extremely flammable gas
Precautionary statements: P203, P210, P222, P280, P377, P381, P403
View all classifications (6)
- [6] Regulation (EC) No 1272/2008 of the European Parliament and of the Council · DangerH220
- [7] European Chemicals Agency (ECHA) · 789 reports · DangerH220, H280
- [7] European Chemicals Agency (ECHA) · 605 reports · DangerH220, H280
- [7] European Chemicals Agency (ECHA) · 58 reportsH412
- [4] Hazardous Substances Data Bank (HSDB) · DangerH220, H280
- [4] Hazardous Substances Data Bank (HSDB) · DangerH220, H280
Exposure limits
- TLV: 250 ppm as TWA[3]
First aid
- Excerpt from ERG Guide 115 [Gases - Flammable (Including Refrigerated Liquids)]: Refer to the "General First Aid" section. Specific First Aid: Clothing frozen to the skin should be thawed before being removed. In case of contact with liquefied gas, only medical personnel should attempt thawing frosted parts. In case of burns, immediately cool affected skin for as long as possible with cold water. Do not remove clothing if adhering to skin. (ERG, 2024)[1]
- Fresh air, rest. Artificial respiration may be needed. Refer immediately for medical attention.[3]
- ON frostbite: Rinse with plenty of water, do NOT remove clothes. Refer for medical attention .[3]
- First rinse with plenty of water for several minutes (remove contact lenses if easily possible), then refer for medical attention.[3]
Storage
Incompatibilities
Safety data sheets on the supplier’s page: CATO Research Chemicals Inc., Sigma-Aldrich, Smolecule.
Always read the supplier’s safety data sheet before working with it.
Spectra
- NMRNMRShiftDB
- 13C NMRSpectraBase (VARIAN HA-100)
- GC-MSNIST Mass Spectrometry Data Center · NIST Mass Spectrometry Data Center · NIST Mass Spectrometry Data Center · NIST Mass Spectrometry Data Center · NIST Mass Spectrometry Data Center · NIST Mass Spectrometry Data Center
- Other MSHazardous Substances Data Bank (HSDB)
- UVHazardous Substances Data Bank (HSDB)
- IRHazardous Substances Data Bank (HSDB)
- Vapor Phase IRSpectraBase (Gas cell)
- RamanHazardous Substances Data Bank (HSDB) · SpectraBase
Experimental spectra held by these sources; each link opens the source's own record.
Literature
Reading PubChem, OpenAlex and GSRS…
Bioactivity
Reading ChEMBL…
References
- [1]CAMEO Chemicals · Public domain (NOAA) · via PubChem · retrieved 2026-10-14
- [2]EPA Chemical Data Reporting (CDR) · Public domain (US EPA) · via PubChem · retrieved 2026-10-14
- [3]ILO-WHO International Chemical Safety Cards (ICSCs) · CC BY 4.0 · via PubChem · retrieved 2026-10-14
- [4]Hazardous Substances Data Bank (HSDB) · Public domain (US NLM) · via PubChem · retrieved 2026-10-14
- [5]PAC Chemical Database, U.S. Department of Energy · Public domain (US DOE) · via PubChem · retrieved 2026-10-14
- [6]Regulation (EC) No 1272/2008 of the European Parliament and of the Council · EU reuse policy, CC BY 4.0 · via PubChem · retrieved 2026-10-14
- [7]European Chemicals Agency (ECHA) · ECHA legal notice: reuse with acknowledgement · via PubChem · retrieved 2026-10-14
- [8]NMRShiftDB · Linked only · via PubChem · retrieved 2026-10-14
- [9]SpectraBase · Linked only · via PubChem · retrieved 2026-10-14
- [10]NIST Mass Spectrometry Data Center · Linked only · via PubChem · retrieved 2026-10-14
- ·Calculated values: computed by Athanor with RDKit 2026.09 from the structure.
- ·Literature on PubChem
Data last updated 2026-10-14.