Electronic Transition Expected in Ethene
Electronic Transition Expected in C2H4
The energy order of molecular orbitals of ethene is shown below-
When ethene is exposed to uv-vis light (200-750nm), the electron goes from lower filled to higher vacant molecular orbitals by absorbing energy equal to the energy gap between these two molecular orbitals leading to σ → σ*, π → σ* & π → π* transitions.
We know that σ-bonds are very strong, so the excitation of σ-electron is very difficult because σ → σ* transition involves a high energy process. Therefore, it can be observed in far uv region (> 200 nm).
π → σ* & σ → ℼ* transitions are symmetry forbidden transitions. So, the only allowed transition in ethene is π → π* transition which occurs at ~ λmax value 170 nm. π → π* transition occurs with high probability as both π → π* orbitals lie in xz plane.
Electronic Transition Expected in Butadiene
Electronic Transition Expected in Formaldehyde
