Molecular Formula: C₂₁H₂₆O2
Molecular Weight: 310.44
EINECS: 200-777-8
Density: 1.15 g/cm³ 
Flash Point: 190.8 °C
Melting point: 150-154 ºC
Index of Refraction: 1.591
CAS Registry Number: 72-33-3
Appearance: Crystalline Solid 
Enthalpy of Vaporization: 73.75 kJ/mol 
Boiling Point: 442.3 °C at 760 mmHg 
Vapour Pressure: 1.33E-08 mmHg at 25°C 
IUPAC Name: (8R,9S,13S,14S,17R)-17-ethynyl-3-methoxy-13-methyl-7,8,9,11,12,14,15,16-octahydro-6H-cyclopenta[a]phenanthren-17-ol
Synonyms: (+)-17-Alpha-ethynyl-17-beta-hydroxy-3-methoxy-1,3,5(10)-estratriene ; (17-alpha)-3-methoxy-19-norpregna-1,3,5(10)-trien-20-yn-17-ol ; 17aethynyl-estradiol-3-methylether ; 17alpha-19-Norpregna-1,3,5(10)-trien-20-yn-17-ol, 3-methoxy-
Following is the molecular structure of 3-Methylethynylestradiol (CAS NO. 72-33-3):

 3-Methylethynylestradiol (CAS NO. 72-33-3) is a orally active estrogenic steroid. It was the estrogen used in many of the first oral contraceptives.

NTP 10th Report on Carcinogens. IARC Cancer Review: Human Limited Evidence IMEMDT    IARC Monographs on the Evaluation of Carcinogenic Risk of Chemicals to Man . 21 ,1979,p. 257.(World Health Organization, Internation Agency for Research on Cancer,Lyon, France.: ) (Single copies can be ordered from WHO Publications Centre U.S.A., 49 Sheridan Avenue, Albany, NY 12210) ; Animal Sufficient Evidence IMEMDT    IARC Monographs on the Evaluation of Carcinogenic Risk of Chemicals to Man . 6 ,1974,p. 87.(World Health Organization, Internation Agency for Research on Cancer,Lyon, France.: ) (Single copies can be ordered from WHO Publications Centre U.S.A., 49 Sheridan Avenue, Albany, NY 12210) ; IMEMDT    IARC Monographs on the Evaluation of Carcinogenic Risk of Chemicals to Man . 21 ,1979,p. 257.(World Health Organization, Internation Agency for Research on Cancer,Lyon, France.: ) (Single copies can be ordered from WHO Publications Centre U.S.A., 49 Sheridan Avenue, Albany, NY 12210) .

Confirmed carcinogen with experimental neoplastigenic, tumorigenic, and teratogenic data. Moderately toxic by subcutaneous route. Human reproductive effects by ingestion: changes in ovaries and fallopian tubes, fertility effects. Experimental reproductive effects. Mutation data reported. An FDA proprietary drug. A steroid used in oral contraceptives. When heated to decomposition it emits acrid smoke and irritating fumes.
Safety Information
Hazard Codes: Xn 
Risk Statements: 36/37/38-40-48-68 
R36/37/38: Irritating to eyes, respiratory system and skin. 
R40: Limited evidence of a carcinogenic effect. 
R48: Danger of serious damage to health by prolonged exposure.
R68: Possible risk of irreversible effects.
Safety Statements: 22-26-36/37/39-45-36/37 
S22: Do not breathe dust. 
S26: In case of contact with eyes, rinse immediately with plenty of water and seek medical advice. 
S36/37/39: Wear suitable protective clothing, gloves and eye/face protection. 
S45: In case of accident or if you feel unwell, seek medical advice immediately (show the label whenever possible.) 
S36/37: Wear suitable protective clothing and gloves.
WGK Germany: 3
RTECS: RC8960000