Chemistry informtion about 2-Pentyne (CAS NO.627-21-4) is:
IUPAC Name: Pent-2-Yne
Synonyms: 1-Ethyl-2-Methylacetylene ; C2h5cequivcch3 ; Ethylmethylacetylene ; 2-Pentyne ; Pent-2-Yne ; 2-Pentyne 98% ; 2-Pentyne,98+% ; Valerylene
Product Categories: Miscellaneous ; Acetylenes ; Acetylenic Hydrocarbons ; Alkynes ; Internal ; Organic Building Blocks 
MF: C₅H₈
MW: 68.12
EINECS: 210-989-2 
Density: 0.721 g/cm3
Melting Point: −109 °C(lit.)
Flash Point: °C 
Boiling Point: 56.7 °C at 760 mmHg
Vapour Pressure: 237 mmHg at 25°C 
Enthalpy of Vaporization: 28.71 kJ/mol
Refractive Index: n20/D 1.404(lit.)
Storage temp.: Flammables area
BRN: 1696938
Following is the molecular structure of 2-Pentyne (CAS NO.627-21-4) is:

A very dangerous fire hazard when exposed to heat or flame; can react vigorously with oxidizing materials. Solutions with silver perchlorate explode on contact with mercury. When heated to decomposition it emits acrid smoke and irritating fumes. See also ACETYLENE COMPOUNDS and ALKYNES.
Hazard Codes:
F
Xi
Risk Statements:
R11:Highly flammable. 
R36/37/38:Irritating to eyes, respiratory system and skin.
Safety Statements:
S16:Keep away from sources of ignition. 
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.
RIDADR: UN 3295 3/PG 2
WGK Germany: 3
F:
F 10: Keep under argon.
F 23: Sensitive to air.
HazardClass: 3
PackingGroup: II

2-Pentyne (CAS NO.627-21-4) is an organic compound, is an internal alkyne. It is an isomer of 1-pentyne, a terminal alkyne.Also it is a clear colorless to slightly yellow liquid.
First Aid Measures:
Eyes: Flush eyes with plenty of water for at least 15 minutes, occasionally lifting the upper and lower eyelids. Get medical aid.
Skin: Get medical aid. Flush skin with plenty of water for at least 15 minutes while removing contaminated clothing and shoes.
Ingestion: Get medical aid. Wash mouth out with water.
Inhalation: Remove from exposure and move to fresh air immediately. If not breathing, give artificial respiration. If breathing is difficult, give oxygen. Get medical aid. 
Handling and Storage:
Handling: Use spark-proof tools and explosion proof equipment. Avoid breathing dust, vapor, mist, or gas. Avoid contact with skin and eyes.
Storage: Keep away from sources of ignition. Store in a cool, dry place. Store in a tightly closed container. Flammables-area.