Question

For the hexatriene molecule:

(i) Draw an orbital energy level diagram for the pi-molecular orbitals, clearly indicating which orbitals are occupied.

(ii) Sketch the unoccupied pi-molecular orbitals and their respective symmetries, clearly indicating the location of any existing nodes.

Answer 1

HEXATRIENE MOLECULE

Orbital Energy level diagram for pi molecular orbitals

Here Hexatriene possess 6 pi electrons,comprises of 6 carbon atoms which is sp2 hybridised. These six p orbitals are unused. The six p atomic orbitals will combine to form 6 molecular orbitals. Six electrons will fill these molecular orbitals.

The sign of the p orbitals remains the same from the lower to the higher of nodal plane in 1. We can observe a single change in the middle for 2, and 2 changes for 3. This indicates that when the nodal planes increases, the energy level of the system gets accelerated with increase in the nodes. Where as the number of nodes in 4 is 3, and for 5 is 4. 6 nodes lies between adjacent p orbitals of neighboring carbon atoms.

According to bonding interactions 1 has 5, 2 has 3, 3 has 1. Whereas regarding antibonding interactions 4 has 1, 5 has 3 and 6 has 5. In total there are 9 bonding interactions responsible for energy of hexatriene.