U3-1-3 - Chromophores Flashcards
Explain what is meant by the highest occupied molecular orbital (HOMO).
Highest energy bonding molecular orbital containing electrons.
Explain what is meant by the lowest unoccupied molecular orbital (LUMO).
Lowest antibonding molecular orbital
This orbital does not contain e−
An organic complex is colourless if it only absorbs ______ light.
UV
An organic complex absorbs only UV light. Why is this?
Large energy gap between HOMO and LUMO
Chromophore
A group of atoms within a molecule that is responsible for absorption of light in the visible region of the spectrum.
State what happens to e– when a chromophore absorbs light
An e– is promoted from HOMO to LUMO
Chromophores exist in molecules containing a _______________ _________.
conjugated system
Conjugated system
A system of adjacent unhybridised p orbitals that overlap side-on to form a molecular orbital across a number of C atoms.
What structural feature is present in conjugated systems?
hint: bonds
Alternating single and double bonds
A system of adjacent unhybridised p orbitals that overlap side-on to form a molecular orbital across a number of C atoms.
Conjugated system
Electrons in a conjugated system can be described as __________.
delocalised
How can you compare the sizes of conjugated systems in different molecules?
Count the no. of (alternating) double bonds.
More double bonds = larger conjugated system.
The more atoms in the conjugated system, the ___________ the energy gap between HOMO and LUMO.
smaller
The larger the conjugated system, the _________ the wavelength of light absorbed.
longer (lower E)
When the wavelength of light absorbed is in the visible region, the compound will exhibit the __________________ colour.
complementary
opposite on the colour wheel
