Propyne

Athanor · official

C₃H₄ · 40.06 g/mol

IUPAC name: prop-1-yne

Also called methylacetylene, allylene

Reagents Functional groups

Open in Athanor

Drawn from its SMILES with RDKit

DangerExtremely flammable gas · Contains gas under pressure; may explode if heated · May cause respiratory irritation · May cause drowsiness or dizziness

Names and identifiers

IUPAC name: prop-1-yne
Synonyms: methylacetylene, allylene, Methylacetylene
+ 35 more
prop-1-yne, 1-PROPYNE, Allylene, Methyl acetylene, Acetylene, methyl-, 086L40ET1B, DTXSID0026387, CHEBI:48086, RefChem:6178, DTXCID406387, 200-828-4, METHYLACETYLENE-D1, MFCD00036235, Propyne, ca. 4% in N,N-Dimethylformamide, ca. 1.0mol/L, Propynylidyne, Allylene; Methylacetylene; Propine, CCRIS 6830, HSDB 2508, EINECS 200-828-4, BRN 0878138, UNII-086L40ET1B, Propyne, >=97%, Propyne, >=99%, 1-PROPYNE [HSDB], SCHEMBL2030, SCHEMBL2031, SCHEMBL2901, SCHEMBL65791, 4-01-00-00958 (Beilstein Handbook Reference), CH3C.$.CH, SCHEMBL308202, SCHEMBL345819, SCHEMBL521923, SCHEMBL846698, CHEMBL116902
Molecular formula: C₃H₄
Empirical formula: C₃H₄
Molecular weight: 40.06 g/mol
Exact mass: 40.03130
CAS number: 74-99-7
PubChem CID: 6335
Canonical SMILES: CC#C
Isomeric SMILES: CC#C
InChI: InChI=1S/C3H4/c1-3-2/h1H,2H3
InChIKey: MWWATHDPGQKSAR-UHFFFAOYSA-N
Molfile

Names, InChI and the identifiers from PubChem, retrieved 2026-10-14.

Physical properties

TemperaturePressureDensity

Appearance: Colorless gas [Note: Shipped as a liquefied compressed gas].[6]
6 values
From Hazardous Substances Data Bank (HSDB), the most authoritative source here.
Value As written Source
– 1-propyne appears as a colorless liquefied gas with a sweet odor. mp: -104 °C, bp: -23.1 °C. Insoluble in water, soluble in ethanol, chloroform and benzene. Moderately toxic by inhalation. Used as a specialty fuel. Denser than air. Vapors may ignite at distant sources of ignition and flash back. [1] CAMEO Chemicals
– Liquid; Gas Vapor [2] EPA Chemical Data Reporting (CDR)
– COLOURLESS COMPRESSED GAS WITH CHARACTERISTIC ODOUR. [3] ILO-WHO International Chemical Safety Cards (ICSCs)
– Colorless gas with a sweet odor. [4] Occupational Safety and Health Administration (OSHA)
– Colorless gas with a sweet odor. [Note: A fuel that is shipped as a liquefied compressed gas.] [5] The National Institute for Occupational Safety and Health (NIOSH)
–shown Colorless gas [Note: Shipped as a liquefied compressed gas]. [6] Hazardous Substances Data Bank (HSDB)cites NIOSH. NIOSH Pocket Guide to Chemical Hazards & Other Databases CD-ROM. Department of Health & Human Services, Centers for Disease Prevention & Control. National Institute for Occupational Safety & Health. DHHS (NIOSH) Publication No. 2005-151 (2005)
Odor: Sweet odor[6]
Melting point: -102.7 °C[3]
6 values
6 of 6 sources agree on it (most common value).
Value As written Source
−103 °C -153 °F (NIOSH, 2024) [1] CAMEO Chemicals
−102.7 °C -102.7 °C [6] Hazardous Substances Data Bank (HSDB)cites Lide, D.R., G.W.A. Milne (eds.). Handbook of Data on Organic Compounds. Volume I. 3rd ed. CRC Press, Inc. Boca Raton ,FL. 1994., p. V5: 4591
−102.7 °Cshown -102.7 °C [3] ILO-WHO International Chemical Safety Cards (ICSCs)
−103 °C -153 °F [4] Occupational Safety and Health Administration (OSHA)
−102.7 °C -102.7 °C [7] PAC Chemical Database, U.S. Department of Energy
−103 °C -153 °F [5] The National Institute for Occupational Safety and Health (NIOSH)
Boiling point: -23.2 °C[3]
6 values
6 of 6 sources agree on it (most common value).
Value As written Source
−23 °C -10 °F at 760 mmHg (NIOSH, 2024) [1] CAMEO Chemicals
−23.2 °C -23.2 °C [6] Hazardous Substances Data Bank (HSDB)cites Lide, D.R., G.W.A. Milne (eds.). Handbook of Data on Organic Compounds. Volume I. 3rd ed. CRC Press, Inc. Boca Raton ,FL. 1994., p. V5: 4591
−23.2 °Cshown -23.2 °C [3] ILO-WHO International Chemical Safety Cards (ICSCs)
−23 °C -10 °F [4] Occupational Safety and Health Administration (OSHA)
−23.3 °C -23.3 °C @760 [mm Hg] [7] PAC Chemical Database, U.S. Department of Energy
−23 °C -10 °F [5] The National Institute for Occupational Safety and Health (NIOSH)
Density: 0.607 at 25 °C/4 °C[6]
3 values
Only one source reports it.
Value As written Source
0.607 g/mLshown 0.607 at 25 °C/4 °C [6] Hazardous Substances Data Bank (HSDB)cites Lide, D.R., G.W.A. Milne (eds.). Handbook of Data on Organic Compounds. Volume I. 3rd ed. CRC Press, Inc. Boca Raton ,FL. 1994., p. V5: 4591
– Relative density (water = 1): 0.70 [3] ILO-WHO International Chemical Safety Cards (ICSCs)
– 1.41(relative gas density) [5] The National Institute for Occupational Safety and Health (NIOSH)
2 more values were reported but failed the checks (unreadable or out of range), so they are not shown.
Solubility in water: Solubility in water, g/100ml: 0.36[3]
5 values
From ILO-WHO International Chemical Safety Cards (ICSCs), the most authoritative source here.
Value As written Source
– Insoluble (NIOSH, 2024) [1] CAMEO Chemicals
– In water, 3,640 mg/L at 25 °C [6] Hazardous Substances Data Bank (HSDB)cites McAuliffe C; J Phys Chem 70: 1267-75 (1966)
– Very sol in alcohol; sol in chloroform, benzene [6] Hazardous Substances Data Bank (HSDB)cites Lide, D.R., G.W.A. Milne (eds.). Handbook of Data on Organic Compounds. Volume I. 3rd ed. CRC Press, Inc. Boca Raton ,FL. 1994., p. V5: 4591
–shown Solubility in water, g/100ml: 0.36 [3] ILO-WHO International Chemical Safety Cards (ICSCs)
– Insoluble [5] The National Institute for Occupational Safety and Health (NIOSH)
log P: log Kow = 0.94[6]
Vapor pressure: 4310 [mmHg] @25 °C[7]
2 values
Sources disagree; from PAC Chemical Database, U.S. Department of Energy, the most authoritative.
Value As written Source
3900 mmHg Vapor pressure, kPa at 20 °C: 521 [3] ILO-WHO International Chemical Safety Cards (ICSCs)
4310 mmHgshown 4310 [mm Hg] @25 °C [7] PAC Chemical Database, U.S. Department of Energy
4 more values were reported but failed the checks (unreadable or out of range), so they are not shown.
Viscosity: Reported, but no value passed the checks.
The 2 values and why
gas at 298 deg K: 8.4X10-3 mPa-s (could not be read; source [6])
liquid at 233 deg K: 0.26 mPa-s (could not be read; source [6])
Refractive index: Index of refraction = 1.3863 at -40 °C/D[6]

Value	As written	Source
–	1-propyne appears as a colorless liquefied gas with a sweet odor. mp: -104 °C, bp: -23.1 °C. Insoluble in water, soluble in ethanol, chloroform and benzene. Moderately toxic by inhalation. Used as a specialty fuel. Denser than air. Vapors may ignite at distant sources of ignition and flash back.	[1] CAMEO Chemicals
–	Liquid; Gas Vapor	[2] EPA Chemical Data Reporting (CDR)
–	COLOURLESS COMPRESSED GAS WITH CHARACTERISTIC ODOUR.	[3] ILO-WHO International Chemical Safety Cards (ICSCs)
–	Colorless gas with a sweet odor.	[4] Occupational Safety and Health Administration (OSHA)
–	Colorless gas with a sweet odor. [Note: A fuel that is shipped as a liquefied compressed gas.]	[5] The National Institute for Occupational Safety and Health (NIOSH)
–shown	Colorless gas [Note: Shipped as a liquefied compressed gas].	[6] Hazardous Substances Data Bank (HSDB)cites NIOSH. NIOSH Pocket Guide to Chemical Hazards & Other Databases CD-ROM. Department of Health & Human Services, Centers for Disease Prevention & Control. National Institute for Occupational Safety & Health. DHHS (NIOSH) Publication No. 2005-151 (2005)

Value	As written	Source
−103 °C	-153 °F (NIOSH, 2024)	[1] CAMEO Chemicals
−102.7 °C	-102.7 °C	[6] Hazardous Substances Data Bank (HSDB)cites Lide, D.R., G.W.A. Milne (eds.). Handbook of Data on Organic Compounds. Volume I. 3rd ed. CRC Press, Inc. Boca Raton ,FL. 1994., p. V5: 4591
−102.7 °Cshown	-102.7 °C	[3] ILO-WHO International Chemical Safety Cards (ICSCs)
−103 °C	-153 °F	[4] Occupational Safety and Health Administration (OSHA)
−102.7 °C	-102.7 °C	[7] PAC Chemical Database, U.S. Department of Energy
−103 °C	-153 °F	[5] The National Institute for Occupational Safety and Health (NIOSH)

Value	As written	Source
−23 °C	-10 °F at 760 mmHg (NIOSH, 2024)	[1] CAMEO Chemicals
−23.2 °C	-23.2 °C	[6] Hazardous Substances Data Bank (HSDB)cites Lide, D.R., G.W.A. Milne (eds.). Handbook of Data on Organic Compounds. Volume I. 3rd ed. CRC Press, Inc. Boca Raton ,FL. 1994., p. V5: 4591
−23.2 °Cshown	-23.2 °C	[3] ILO-WHO International Chemical Safety Cards (ICSCs)
−23 °C	-10 °F	[4] Occupational Safety and Health Administration (OSHA)
−23.3 °C	-23.3 °C @760 [mm Hg]	[7] PAC Chemical Database, U.S. Department of Energy
−23 °C	-10 °F	[5] The National Institute for Occupational Safety and Health (NIOSH)

Value	As written	Source
0.607 g/mLshown	0.607 at 25 °C/4 °C	[6] Hazardous Substances Data Bank (HSDB)cites Lide, D.R., G.W.A. Milne (eds.). Handbook of Data on Organic Compounds. Volume I. 3rd ed. CRC Press, Inc. Boca Raton ,FL. 1994., p. V5: 4591
–	Relative density (water = 1): 0.70	[3] ILO-WHO International Chemical Safety Cards (ICSCs)
–	1.41(relative gas density)	[5] The National Institute for Occupational Safety and Health (NIOSH)

Value	As written	Source
–	Insoluble (NIOSH, 2024)	[1] CAMEO Chemicals
–	In water, 3,640 mg/L at 25 °C	[6] Hazardous Substances Data Bank (HSDB)cites McAuliffe C; J Phys Chem 70: 1267-75 (1966)
–	Very sol in alcohol; sol in chloroform, benzene	[6] Hazardous Substances Data Bank (HSDB)cites Lide, D.R., G.W.A. Milne (eds.). Handbook of Data on Organic Compounds. Volume I. 3rd ed. CRC Press, Inc. Boca Raton ,FL. 1994., p. V5: 4591
–shown	Solubility in water, g/100ml: 0.36	[3] ILO-WHO International Chemical Safety Cards (ICSCs)
–	Insoluble	[5] The National Institute for Occupational Safety and Health (NIOSH)

Value	As written	Source
3900 mmHg	Vapor pressure, kPa at 20 °C: 521	[3] ILO-WHO International Chemical Safety Cards (ICSCs)
4310 mmHgshown	4310 [mm Hg] @25 °C	[7] PAC Chemical Database, U.S. Department of Energy

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: 3
Rings: 0
Aromatic rings: 0
Fraction sp³ carbons (Fsp3): 0.33
H-bond donors: 0
H-bond acceptors: 0
Rotatable bonds: 0
TPSA (Å²): 0
Formal charge: 0
XLogP3: 0.9 PubChem
Complexity: 26 PubChem
Stereocenters: None
Double-bond geometry: None specified
Point group: C3v of one 3D conformer with its hydrogens, by Athanor’s engine (as in the app)

Elemental analysis

C89.94%
H10.06%

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: 0.64 Crippen (Wildman and Crippen 1999)
log S (water solubility): -0.49 ESOL (Delaney 2004), log mol/L
Synthetic accessibility: 3.66 SA score, 1 easy to 10 hard (Ertl and Schuffenhauer 2009)

Drug-likeness: Lipinski’s rule of five

Molecular weight ≤ 500: 40.07
log P ≤ 5 (Crippen): 0.64
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

Most widely reported: 346 company reports to ECHA. Source [8].

Flammable
Compressed gas
Harmful or irritant

NFPA 704[6]

H220Extremely flammable gas (98.8% of reports)
H280Contains gas under pressure; may explode if heated
H335May cause respiratory irritation (52.9% of reports)
H336May cause drowsiness or dizziness (34.7% of reports)

Precautionary statements: P203, P210, P222, P261, P271, P280, P304+P340, P319, P377, P381, P403, P403+P233, P405, P410+P403, P501

Exposure limits

PEL-TWA (8-Hour Time Weighted Average): 1000 ppm (1650 mg/m³)[4]
PEL: TWA 1000 ppm (1650 mg/m3)[5]
TLV: 1000 ppm as TWA[3]
TLV-TWA (Time Weighted Average): 1000 ppm (EX) [1956][4]
IDLH: 1700 ppm ; Based on 10% of the lower explosive limit. (NIOSH, 2024)[1]
IDLH: 1700 ppm [Based on 10% of the lower explosion limit for safety considerations even though the relevant toxicological data indicated that irreversible health efects or impairment of escape existed only at higher concentrations.][6]

First aid

Excerpt from NIOSH Pocket Guide for Methyl acetylene: Eye: Frostbite - If eye tissue is frozen, seek medical attention immediately; if tissue is not frozen, immediately and thoroughly flush the eyes with large amounts of water for at least 15 minutes, occasionally lifting the lower and upper eyelids. If irritation, pain, swelling, lacrimation, or photophobia persist, get medical attention as soon as possible. Skin: Frostbite - If frostbite has occurred, seek medical attention immediately; do NOT rub the affected areas or flush them with water. In order to prevent further tissue damage, do NOT[1]
(General first aid procedures) Eye: Frostbite - If eye tissue is frozen, seek medical attention immediately; if tissue is not frozen, immediately and thoroughly flush the eyes with large amounts of water for at least 15 minutes, occasionally lifting the lower and upper eyelids. If irritation, pain, swelling, lacrimation, or photophobia persist, get medical attention as soon as possible. Skin: Frostbite - Compressed gases may create low temperatures when they expand rapidly. Leaks and uses that allow rapid expansion may cause a frostbite hazard.[5]
Fresh air, rest. Artificial respiration may be needed. Refer for medical attention.[3]
ON frostbite: Rinse with plenty of water, do NOT remove clothes.[3]

Storage

Fireproof. Cool.[3]

Incompatibilities

Can react vigorously with oxidizing materials.[6]
Strong oxidizers (such as chlorine), copper alloys [Note: Can decompose explosively at 4.5 to 5.6 atmospheres of pressure].[6]
Methyl acetylene forms compounds with copper and copper alloys that are very sensitive to shock.[6]
Strong oxidizers (such as chlorine), copper alloys [Note: Can decompose explosively at 4.5 to 5.6 atmospheres of pressure.][5]

Safety data sheets on the supplier’s page: abcr GmbH, AKos Consulting & Solutions, A2B Chem.

Always read the supplier’s safety data sheet before working with it.

Spectra

NMRHazardous Substances Data Bank (HSDB) · NMRShiftDB
13C NMRSpectraBase
GC-MSNIST Mass Spectrometry Data Center · SpectraBase
Other MSHazardous Substances Data Bank (HSDB)
Vapor Phase IRSpectraBase (Vapor Phase)

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]Occupational Safety and Health Administration (OSHA) · Public domain (US DOL) · via PubChem · retrieved 2026-10-14
[5]The National Institute for Occupational Safety and Health (NIOSH) · Public domain (US CDC) · via PubChem · retrieved 2026-10-14
[6]Hazardous Substances Data Bank (HSDB) · Public domain (US NLM) · via PubChem · retrieved 2026-10-14
[7]PAC Chemical Database, U.S. Department of Energy · Public domain (US DOE) · via PubChem · retrieved 2026-10-14
[8]European Chemicals Agency (ECHA) · ECHA legal notice: reuse with acknowledgement · via PubChem · retrieved 2026-10-14
[9]NMRShiftDB · Linked only · via PubChem · retrieved 2026-10-14
[10]SpectraBase · Linked only · via PubChem · retrieved 2026-10-14
[11]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.