Triple bond
Three bonding components connect the same carbon pair.
One σ bond is accompanied by two π bonds.
Molecular compound · alkyne
Ethyne
C₂H₂
Ethyne is C₂H₂, the simplest alkyne. Its two carbon atoms are connected by a triple bond containing one σ bond and two mutually perpendicular π components.
Name note: ethyne and acetylene name the same compound.
Essentials
The C≡C triple bond defines ethyne as an alkyne.
H–C≡C–H is a compact molecule with one σ and two π bonding components between the carbon atoms.
Detail
Ethyne is linear: H–C≡C–H lies on one axis.
Each carbon has two principal σ-bond directions, giving 180° geometry in the standard local bonding model.
Two π systems
The two π components occupy perpendicular orbital planes.
The σ framework lies along the molecular axis.
Understand
Hydrogenation can reduce a triple bond stepwise.
Adding hydrogen can move from ethyne toward ethene and then ethane. Selectivity depends on catalyst and conditions.
Bond-order series
Ethane, ethene and ethyne form a clean single/double/triple comparison.
Increasing bond order changes geometry, rotation and reactivity.
Reference identifiers
Names and identifiers that pin down the chemical identity.
| Formula | C₂H₂ / HC≡CH |
|---|---|
| CAS Registry Number | 74-86-2 |
| PubChem CID | 6326 |
Advanced
Push past the first model without losing the simple picture.
Why is ethyne linear?
Each carbon has two sigma-bond directions arranged 180° apart, while two p-orbital pairs form the π bonds.
Why are terminal alkyne hydrogens more acidic than alkene hydrogens?
The conjugate-base electron pair resides on a carbon orbital with greater s character, stabilizing negative charge relative to sp2 or sp3 carbon.
Is acetylene a different substance from ethyne?
No. Acetylene is the common retained name for ethyne.
Constituent elements