Conjugated dienes are chromophores which contribute colors to a compound by light absorption.
The greater the conjugation and resonance, the longer the wavelength absorbed by the compound.
When electrons absorb energy, they transition from a lower energy orbital to a higher energy orbital.
Highest Occupied Molecular Orbital (HOMO) → Lowest Unoccupied Molecular Orbital (LUMO)
Suppose you have two unlabeled flasks, and each flask contains one of these two compounds:
Can you differentiate the compounds using a UV spectrophotometer? Select the true statement.
a. The λmax of the compound with 2 conjugated bonds appears at a longer wavelength than does the λmax of the compound with 3 conjugated bonds.
b. The λmax of the compound with 3 conjugated bonds appears at a longer wavelength than does the λmax of the compound with 2 conjugated bonds.
c. The two compounds cannot be differentiated by their λmax values.
Frequently Asked Questions
What scientific concept do you need to know in order to solve this problem?
Our tutors have indicated that to solve this problem you will need to apply the HOMO/LUMO concept. If you need more HOMO/LUMO practice, you can also practice HOMO/LUMO practice problems.