Molecular structure of 2-Hydroxy-3-butynoic acid (CAS NO.38628-65-8) is:

Product Name: 2-Hydroxy-3-butynoic acid
CAS Registry Number: 38628-65-8
Molecular Formula: C₄H₄O₃
Molecular Weight: 100.07
Index of Refraction: 1.518 
Molar Refractivity: 21.46 cm³ 
Molar Volume: 70.8 cm³
Surface Tension: 71.7 dyne/cm 
Density: 1.412 g/cm³ 
Flash Point: 137.2 °C 
Enthalpy of Vaporization: 60.17 kJ/mol 
Boiling Point: 279.7 °C at 760 mmHg
Vapour Pressure: 0.000477 mmHg at 25 °C 
Storage temp.: Freezer
Product Categories: Acetylenes;Acetylenic Alcohols & Their Derivatives;Acetylenic Carboxylic Acids & Their Derivatives
SMILES: O=C(O)C(C#C)O 
InChI: InChI=1/C4H4O3/c1-2-3(5)4(6)7/h1,3,5H,(H,6,7)
InChIKey: LWNHDEQKHFRYMD-UHFFFAOYAN 
Std. InChI: InChI=1S/C4H4O3/c1-2-3(5)4(6)7/h1,3,5H,(H,6,7)
Std. InChIKey: LWNHDEQKHFRYMD-UHFFFAOYSA-N

 2-Hydroxy-3-butynoic acid , its cas register number is 38628-65-8. It also can be called 2-Hydroxybut-3-ynoic acid .