Molecules & Colour Flashcards
How do most organic molecules appear?
Colourless as they absorb from the visible spectrum
What is the energy from photons used to do?
Promote electrons from bonding or non-bonding orbitals into the higher energy antibonding orbitals
What do pi and sigma orbitals contain more of?
Normal bonding pairs of electrons
What do non-bonding orbitals contain?
Lone pairs of electrons
What do the pi and sigma antibonding orbitals contain?
They are normally empty
What type of organic compounds are colourless?
Ones that contain only sigma bonds
What is the highest occupied molecular orbital?
The sigma bonding orbital is the HOMO
What orbital is the lowest unoccupied molecular orbital?
The sigma* antibonding orbital is the LUMO
What can be said about the transition from sigma to sigma*?
The energy transitions involved in promoting an electron is very large
What are conjugated systems?
Organic molecules that are coloured containing delocalised electrons spread over a number of atoms
Why is benzene drawn with a circle in the middle?
The circle represents the delocalised electrons
What must be said for bonds to be conjugated in long carbon chains?
Alternating double and single bonds must be present
What is a chromophore?
A group of atoms within a molecule that is responsible for colour
What can we discover from comparing chromophores?
We can find out about the energy of light that is being absorbed
How can different colours in chromophores be explained?
The colours we observe are not absorbed by the molecules. If the chromophore absorbs light of one colour, then the complementary colour is observed
