Isolobal Analogy Exercises

Some of these questions are explained in the assigned lecture by Roald Hoffman, so please make sure you have done the reading before working out your answers.
  1. Use the interaction diagram on page 40 of Hoffman's lecture to understand the bonding between trimethylenemethane (TMM) and Fe(CO)3. Note that the complex between TMM and Fe(CO)3 has C3v symmetry. From the diagram, how many electrons are in the frontier region of TMM prior to interaction with Fe(CO)3?
  2. How many electrons coming from Fe(CO)3 get involved in bonding interactions with TMM?
  3. What is the ligand bond number of TMM in the complex (TMM)Fe(CO)3?
  4. Using Mulliken symbols appropriate to the C3v point group, what are the symmetry types of the bonds formed between Fe(CO)3 and TMM?
  5. The interaction diagram on page 40 of Hoffman's lecture reveals an equivalence between valence bond and MO treatments for the electronic structure of the Fe(CO)3 fragment. Comment on how this is graphically porgrayed in the diagram.
  6. To what ligand classification does TMM belong?
  7. Use the CBC method to assign (TMM)Fe(CO)3 to its correct class.
  8. Explain how it is that a C2v Fe(CO)4 fragment is isolobal with methylene.
  9. What is the simple organic fragment to which C3v Co(CO)3 is isolobal?
  10. It is shown in Hoffman's lecture that d10 ML2 is isolobal with d8 ML4 (both in C2v symmetry). Make a diagram showing where the hybrids point for d10 ML2, and also make a completely labeled energy level diagram representing the corresponding frontier orbitals.

For credit, hand in completed work to your TA any time before April 7.

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