Chemistry 336 Final Exam
Winter 1998 200 pts Name ___________________________________

Note: The last page of the exam is a list of organic starting materials, inorganic reagents and spectral tables to be used for the exam.

1. (18 pts) The reaction of the diene below with HBr gives two isomeric products:

(a) Draw the chemical structures of the two isomers:

(b) Draw the chemical structure of the intermediate of this reaction including all major resonance forms:

(c) Indicate which of the two isomers is the kinetic product and explain your reasoning using the structure of the intermediate.

2. (15 pts) Consider the cation and anion of 1,3,5-cycloheptatriene shown below:

(a) Indicate which one of the two ions is aromatic.

(b) Sketch a molecular orbital energy diagram of the p-system for each ion showing which orbitals are occupied. You do not need to draw the orbitals themselves, just the relative energy levels for the p and p* orbitals. Use your molecular orbital diagram to explain why the one ion you've chosen in part (a) is aromatic.

3. (16 pts) Suggest a plausible mechanism for the following reaction using arrow formalism. Your mechanism must include each step and illustrate explicitly where electrons and atoms are participating in the reaction.

4. (16 pts) 4-methoxypyridine is a stronger base than 3-methoxypyridine:

(a) Draw the chemical structure of the protonated form of 4-methoxypyridine. Draw the resonance form that explains how the 4-methoxy substituent stabilizes the acid form.

(b) Explain why 3-methoxypyridine is a weaker base than 4-methoxypyridine.

(c) Predict whether the rotational barrier about the C--O bond (shown) for the acid form of 4-methoxypyridine is higher or lower than for the acid form of 3-methoxypyridine. Explain your answer.

5. (16 pts) For each of the following chemical reactions, fill in the box with the reagent needed to complete the reaction.

7. (28 pts) For each of the following reactions draw the chemical structure of the expected product(s). Indicate stereochemistry if relevant.

8. (16 pts) For the following synthesis, provide the chemical structure for the intermediate A molecule and the final product. Also fill in the reagents numbered 1 and 2 at the third step of the synthesis. DIEA is an abbreviation for diisopropyl ethylamine and Tos is an abbreviation for toluenesulfonyl.

9. (12 pts) Consider the reaction scheme shown below. Draw the structure of the intermediate A and use it to explain how the product is formed.

10. (15 pts) Complete the following synthesis by providing the chemical structures for the product of each reaction.

11. (12 pts) Consider the two chair-conformations of the cyclohexanone shown below:

(a) Indicate which of the two conformers, A or B, is expected to be of lower energy. Explain your answer.

(b) Predict which of the two alpha protons, Ha or Hb, would be expected to exchange faster upon exposure to NaOD in D₂O. Explain your answer.

12. (18 pts) Propose a plausible synthesis for the molecule below. For starting materials you are to use only those organic molecules in the Toobox (last page of exam) and any inorganic reagents.