In: Chemistry
How do I identify HOMO and LUMO when given orbitals
You can predict this by applying the concept of Linear combination of Atomic Orbital (LCAO) which states that
atomic orbital combines to form molecular orbital half of which is bonding and half of which is anti bonding
so lets start with butadiene it has 4 sp2 carbon in whichone unhybridized p orbital is present on each carbon hence 4 p orbitals combine to form 4 molecular orbital out of which two are bonding and 2 are anti bonding
The highest energy of the bonding orbital will be HOMO and the lowestenergy of the anti bonding orbital will be LUMO ( you can also predict this by taking nodes of the molecular orbital) for n orbitals there will be n-1 node
so in the HOMO which is 2nd orbial nodes will be 1
and in LUMO which is 3rd orbial nodes will be 2