Alkynes: Molecular Orbital Model
Molecular orbital theory (MO theory) combines atomic or hybrid orbitals (AOs) to molecular orbitals (MOs). The hybrid orbitals combine and form a bonding σ orbital and an antibonding σ* orbital. The four p atomic orbitals form two π and two π* molecular orbitals. The energy sequence from the lowest to the highest MO is σ < π(y) = π(z) < π(y)* = π(z)* < σ*. Overall, six electrons are available to occupy the molecular orbitals, e.g. only bonding orbitals are filled.