View
p orbitals
π bond
π* (antibonding)
Molecule
Ethene
1,2-Dichloroethene
Twist about C=C (θ)
0°
Show
Animate twist
σ bond
Nodal planes
Spin
Side-on overlap
θ = 0°
100%
p–p overlap
∝ |cos θ|
270
π bond left
kJ mol⁻¹
0
energy cost
kJ mol⁻¹
Left: π / π* levels (2 electrons). Right: energy cost ≈ 270 sin²θ kJ mol⁻¹ — simple model, π-bond energy ∝ overlap².