Oxygen

Some of these questions are explained in the assigned readings, so please make sure you have done the reading before working out your answers.
  1. Make a sketch of the photoelectron spectrum of O2 and assign the peaks.
  2. In the 1Δg state of O2, is it correct to say that the most energetic electrons are paired up in an antibonding MO? Explain.
  3. What is the degeneracy of the 1Δg state of O2 and what the origin of this degeneracy (i.e., orbital or spin)?
  4. What is the term symbol for the electronic state of O2 having both πg molecular orbitals singly occupied with electrons of opposite spin?
  5. Make a sketch of the Jablonski diagram from your reading, and highlight the crucial spin-conserving reaction that results in singlet oxygen.
  6. What is the term symbol for singlet oxygen produced by reaction of a photo-excited sensitizer with triplet oxygen?
  7. Sixteen wave functions stem from the following excited oxygen configuration: (1σg)2(1σu)2(2σg)2(1πu)3(1πg)3. From a direct product table we note that Πu times Πg gives Σu+ + Σu- + Δu. None of the singlets or triplets derived from these orbital configurations violates the Pauli exclusion principle. Write down the six term symbols for the six electronic states arising from this excited configuration of O2, and verify that the total degeneracy is 16.
  8. Write down the ground configuration for ozone according to the calculated MO picture for this molecule.
  9. When all occupied orbitals are fully occupied in the ground configuration of a molecule, this represents a totally symmetric distribution of the electrons. This is the case for the ozone molecule. What is the term symbol for the ground electronic state of the ozone molecule?
  10. Ozonolysis of an alkene is thought to have as its first step a concerted interaction involving mainly the ozone LUMO and the alkene HOMO. Sketch the latter two orbitals. Take the alkene is to be ethylene and now sketch out the transition state structure (TSS) for this reaction. One possibility is that the TSS has C2v symmetry, while an alternative TSS has Cs symmetry. Explain which one you think it is, and why.
  11. The initial intermediate produced upon reaction of ozone with an alkene is called an ozonide. This species has a 5-membered ring resulting from addition of 1,3 addition of ozone to the alkene; draw the ozonide resulting from reaction of ethylene with ozone.
  12. How many nodes does the 2a1 MO of ozone have? Would you characterize it as a bonding MO? Comment on why this MO is so low in energy.