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Paracetamol

Athanor · official

C8H9NO2 · 151.16 g/mol

IUPAC name: N-(4-hydroxyphenyl)acetamide

Also called acetaminophen, Tylenol, Panadol, APAP, Calpol

Drugs
Open in Athanor
The structure of Paracetamol
Drawn from its SMILES with RDKit
Harmful or irritantWarningHarmful if swallowed · Causes skin irritation · Causes serious eye irritation · Harmful to aquatic life with long lasting effects

Names and identifiers

IUPAC name
N-(4-hydroxyphenyl)acetamide
Synonyms
acetaminophen, Tylenol, Panadol
+ 35 more

APAP, Calpol, 4-Acetamidophenol, N-(4-Hydroxyphenyl)acetamide, 4'-Hydroxyacetanilide, Datril, N-Acetyl-p-aminophenol, Acetaminofen, Algotropyl, p-Acetamidophenol, p-Hydroxyacetanilide, Doliprane, Acamol, Anelix, Lonarid, Naprinol, Abensanil, Acetagesic, Acetalgin, Alvedon, Anaflon, Apamide, Clixodyne, Dymadon, Injectapap, Valadol, Alpiny, Amadil, Anhiba, Eneril, Multin, Tempra, Dirox, p-Acetaminophenol, Biocetamol

Molecular formula
C8H9NO2
Empirical formula
C8H9NO2
Molecular weight
151.16 g/mol
Exact mass
151.06333
CAS number
103-90-2
PubChem CID
1983
Canonical SMILES
CC(=O)NC1=CC=C(C=C1)O
Isomeric SMILES
CC(=O)NC1=CC=C(C=C1)O
InChI
InChI=1S/C8H9NO2/c1-6(10)9-7-2-4-8(11)5-3-7/h2-5,11H,1H3,(H,9,10)
InChIKey
RZVAJINKPMORJF-UHFFFAOYSA-N
Molfile

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

Physical properties

TemperaturePressureDensity
Appearance
4-hydroxyacetanilide is an odorless white crystalline solid. Bitter taste. pH (saturated aqueous solution) about 6. (NTP, 1992)[1]
2 values

From CAMEO Chemicals, the most authoritative source here.

ValueAs writtenSource
–shown4-hydroxyacetanilide is an odorless white crystalline solid. Bitter taste. pH (saturated aqueous solution) about 6. (NTP, 1992)[1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
–COLOURLESS CRYSTALS OR CRYSTALLINE POWDER.[2] ILO-WHO International Chemical Safety Cards (ICSCs)
Odor
Odorless[3]
Melting point
169-170 °C[2]
2 values

2 of 2 sources agree on it (most common value).

ValueAs writtenSource
169 to 172 °C336 to 342 °F (NTP, 1992)[1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
169 to 170 °Cshown169-170 °C[2] ILO-WHO International Chemical Safety Cards (ICSCs)
Boiling point
>500 °C[2]
Density
1.293 at 21 °C (70 °F) (NTP, 1992) - Denser than water[1]
2 values

2 of 2 sources agree on it (most common value).

ValueAs writtenSource
–shown1.293 at 70 °F (NTP, 1992) - Denser than water[1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
–1.3 g/cm³[2] ILO-WHO International Chemical Safety Cards (ICSCs)
Solubility in water
Solubility in water, g/100ml at 20 °C: 1.4 (moderate)[2]
3 values

From ILO-WHO International Chemical Safety Cards (ICSCs), the most authoritative source here.

ValueAs writtenSource
–1 to 5 mg/mL at 72 °F (NTP, 1992)[1] CAMEO Chemicalscites National Toxicology Program, Institute of Environmental Health Sciences, National Institutes of Health (NTP). 1992. National Toxicology Program Chemical Repository Database. Research Triangle Park, North Carolina.
–In water, 14,000 mg/L at 25 °C[3] Hazardous Substances Data Bank (HSDB)cites Yalkowsky, S.H., He, Yan, Jain, P. Handbook of Aqueous Solubility Data Second Edition. CRC Press, Boca Raton, FL 2010, p. 492
–shownSolubility in water, g/100ml at 20 °C: 1.4 (moderate)[2] ILO-WHO International Chemical Safety Cards (ICSCs)
log P
0.49[2]
2 values

Sources disagree; from ILO-WHO International Chemical Safety Cards (ICSCs), the most authoritative.

ValueAs writtenSource
–log Kow = 0.46[3] Hazardous Substances Data Bank (HSDB)cites Sangster J; LOGKOW Database. A databank of evaluated octanol-water partition coefficients (Log P). Available from, as of Mar 6, 2014: https://logkow.cisti.nrc.ca/logkow/search.html
–shown0.49[2] ILO-WHO International Chemical Safety Cards (ICSCs)
pKa
pKa = 9.38[3]
Vapor pressure
6.29 × 10⁻⁵ mmHg at 25 °C[3]
Autoignition temperature
540 °C[2]

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
11
Rings
1
Aromatic rings
1
Fraction sp³ carbons (Fsp3)
0.12
H-bond donors
2
H-bond acceptors
2
Rotatable bonds
1
TPSA (Ų)
49.3
Formal charge
0
XLogP3
0.5 PubChem
Complexity
139 PubChem
Stereocenters
None
Double-bond geometry
None specified
Point group
C1 of one 3D conformer with its hydrogens, by Athanor’s engine (as in the app)

Elemental analysis

  • C63.56%
  • H6.00%
  • N9.27%
  • O21.17%

Isotope pattern

100%151.0639.2%152.066153.069

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
1.35 Crippen (Wildman and Crippen 1999)
log S (water solubility)
-1.97 ESOL (Delaney 2004), log mol/L
Synthetic accessibility
1.41 SA score, 1 easy to 10 hard (Ertl and Schuffenhauer 2009)

Drug-likeness: Lipinski’s rule of five

  • Molecular weight ≤ 500: 151.16
  • log P ≤ 5 (Crippen): 1.35
  • H-bond donors ≤ 5: 2
  • H-bond acceptors ≤ 10: 2

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

Warning

Most widely reported: 432 company reports to ECHA. Source [4].

  • Harmful or irritant
  • H302Harmful if swallowed (98.1% of reports)
  • H315Causes skin irritation (17.4% of reports)
  • H319Causes serious eye irritation (17.1% of reports)
  • H412Harmful to aquatic life with long lasting effects (36.8% of reports)

Precautionary statements: P264, P264+P265, P270, P273, P280, P301+P317, P302+P352, P305+P351+P338, P321, P330, P332+P317, P337+P317, P362+P364, P501

View all classifications (3)
  • [4] European Chemicals Agency (ECHA)This chemical does not meet GHS hazard criteria for 1.2% (5 of 432) of reports.
  • [4] European Chemicals Agency (ECHA) · 432 reports · WarningH302, H315, H319, H412
  • [3] Hazardous Substances Data Bank (HSDB) · WarningH302, H315, H319, H335, H401

First aid

  • Eyes: First check the victim for contact lenses and remove if present. Flush victim's eyes with water or normal saline solution for 20 to 30 minutes while simultaneously calling a hospital or poison control center. Do not put any ointments, oils, or medication in the victim's eyes without specific instructions from a physician. Immediately transport the victim after flushing eyes to a hospital even if no symptoms (such as redness or irritation) develop. Skin: Immediately flood affected skin with water while removing and isolating all contaminated clothing.[1]
  • Fresh air, rest.[2]
  • Rinse and then wash skin with water and soap.[2]
  • Rinse with plenty of water (remove contact lenses if easily possible).[2]

Storage

  • Provision to contain effluent from fire extinguishing. Store in an area without drain or sewer access.[2]
  • Keep container tightly closed in a dry and well-ventilated place. Keep in a dry place.[3]
  • Ofirmev should be stored at 20 °C to 25 °C (68 °F to 77 °F). ... Do not refrigerate or freeze.[3]
  • Acetaminophen preparations should be stored at a temperature less than 40 °C, preferably between 15-30 °C; freezing of the oral solution or suspension should be avoided.[3]

Incompatibilities

  • Oxidizing agents[3]

Safety data sheets on the supplier’s page: Aladdin Scientific, Glixx Labs Inc, Allbio Pharm Co., Ltd.

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

Spectra

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. [1]CAMEO Chemicals · Public domain (NOAA) · via PubChem · retrieved 2026-10-14
  2. [2]ILO-WHO International Chemical Safety Cards (ICSCs) · CC BY 4.0 · via PubChem · retrieved 2026-10-14
  3. [3]Hazardous Substances Data Bank (HSDB) · Public domain (US NLM) · via PubChem · retrieved 2026-10-14
  4. [4]European Chemicals Agency (ECHA) · ECHA legal notice: reuse with acknowledgement · via PubChem · retrieved 2026-10-14
  5. [5]NMRShiftDB · Linked only · via PubChem · retrieved 2026-10-14
  6. [6]Human Metabolome Database (HMDB) · Linked only · via PubChem · retrieved 2026-10-14
  7. [7]SpectraBase · Linked only · via PubChem · retrieved 2026-10-14
  8. [8]MassBank of North America (MoNA) · CC BY 4.0 · via PubChem · retrieved 2026-10-14
  9. [9]NIST Mass Spectrometry Data Center · Linked only · via PubChem · retrieved 2026-10-14
  10. [10]MassBank Europe · Linked only · via PubChem · retrieved 2026-10-14
  11. [11]RRUFF Project · Linked only · via PubChem · retrieved 2026-10-14
  12. ·Calculated values: computed by Athanor with RDKit 2026.09 from the structure.
  13. ·Literature on PubChem

Data last updated 2026-10-14.