Question

Explain why the absorbance spectrum on 1,3-butadiene displays an absorption band (217) in the UV region while the absorbance on 1,2-butadiene doesn't display a similar absorption band.

Answer 1

According to quantum mechanics, atoms and molecules can only hold certain defined quantities of energy, or exist in specific states. When such quanta ofelectromagnetic radiation are emitted or absorbed by an atom or molecule, the energy of the radiation changes the state of the atom or molecule from an initial stateto a final state. An absorption band is a range of wavelengths, frequencies or energies in the electromagnetic spectrum which are characteristic of a particular transition from initial to final state in a substance

This fenomena is related to the energy required for a molecule to break its bonds. 1,3-butadiene has a different bond energy than 1,2-butadiene.