U3-1-3 - Chromophores Flashcards
Explain what is meant by the highest occupied molecular orbital (HOMO).
Highest bonding molecular orbital containing e−.
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
