UV absorption in Ethylene (Ethene) and Butadiene


butatdiene orbitals

 



Background:

Click on the diagram to display the various bonding and antibonding molecular orbitals and energies.

  • Energy gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) in butadiene is smaller than in ethylene(ethene)
  • Addition of successive conjugated double bonds progressively narrows the gap between HOMO and LUMO
  • Thus longer wavelength (lower energy) radiation required for the transition

 

 

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