16. Conjugated Systems

Predict the molecular orbitals and identify the HOMO and LUMO orbitals of the following cation.

The pentadienyl radical, H2C=CH-CH=CH-CH2·, has its unpaired electron delocalized over three carbon atoms.

(a) Use resonance forms to show which three carbon atoms bear the unpaired electron.

The pentadienyl radical, H2C=CH-CH=CH-CH2·, has its unpaired electron delocalized over three carbon atoms.

(b) How many MOs are there in the molecular orbital picture of the pentadienyl radical?

(c) How many nodes are there in the lowest-energy MO of the pentadienyl system? How many in the highest-energy MO?

(d) Draw the MOs of the pentadienyl system in order of increasing energy

The pentadienyl radical, H2C=CH-CH=CH-CH2·, has its unpaired electron delocalized over three carbon atoms.

(f) Show how your molecular orbital picture agrees with the resonance picture showing delocalization of the unpaired electron onto three carbon atoms.