EXAM 3

CHEMISTRY 220

Friday, April 26, 2013

NAME (print): ________________________________________________________

TA:_________________ Sect. Day:_________________ Sect. Time:_____________

Fill in the information above. Place your name on the top right of subsequent pages.

Take a few moments to look over the exam. Answer each question on the exam paper.

No calculators, electronic devices, earbuds, texts or notes. You may use molecular models. Important clues and structures are in bold. There is a Periodic Table on pg. 9. Do all preliminary drawing or computations on the work sheets at the end of the exam. The work sheets will not be graded. You may detach the work sheets from the exam.

The exam is 55 minutes.

STOP writing and hand in your exam when you are asked to do so.

Remember: Neatness is to your advantage.

1. (20 pts) Reactions I (3 of 4) ______

2. (20 pts) Reactions II (2 of 3) ______

3. (20 pts) Mechanisms (2 of 4) ______

4. (20 pts) Structure (1 of 2) ______

5. (20 pts) Synthesis ______

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Total (100 pts)

1) Reactions: (20 pts.) Complete 3 of 4 of the following problems. If you do all four, clearly cross out the one you do not want graded. Pay particular attention to stereochemistry and well-defined drawings. Explain briefly.

2) Reactions II: (20 pts.) Complete 2 of 3 of the following problems. Identify the unknown structures. No mechanisms required! If you do all three, clearly cross out the one you do not want graded. Explain briefly. [!!!!! signifies important information!]

…continued

3) Mechanisms: (20 pts.) Complete 2 of 4 of the following questions. If you do 3 or 4, clearly cross out the one(s) you do not want graded.

a) Provide a mechanism (arrow-pushing) for the oxidation of acetaldehyde to acetic acid using aqueous chlorine (Stevens’ oxidation, PS9).

b) Show a method for the preparation of CD₃SCD₂H from CD₃S(O)CD₃ (dimethyl sulfoxide – d₆). [Swern oxidation; class 4/17]

…continued

c) Anhydrous chromium (VI) reagents (Collins’ reagent or PCC) are often used to oxidize primary alcohols to aldehydes. Often esters can be formed, e.g., ethanol ---- > ethyl acetate. Explain and illustrate.

d) The conversion of 2-butene to acetaldehyde by ozonolysis followed by treatment with dimethyl sulfide is a 4-electron oxidation. The same transformation can be accomplished with cat. OsO₄ and periodic acid. i) How many equivalents of periodic acid are required? ii) Explain and illustrate using your knowledge of oxidation levels.

3) Structure: (20 pts.) Complete 1 of 2 of the following problems. If you do both of them, clearly cross out the one you do not want graded. Explain briefly.

a) An optically active ester A (C₁₀H₂₀O₂) reacts with excess LiAlH₄ to provide (±)-B (C₅H₁₂O). Compound A reacts with 2 equiv. of Grignard reagent C (RMgBr) to form (S)-B and (R)-D (C₇H₁₆O). Provide the structures A-D. Explain briefly. [Recall PS9.]

b) Compound A undergoes a two-electron reduction with reagent B to afford C. Compound C reacts with cat. OsO₄/H₂O₂ to yield D. Treatment of D with one equivalent of TsCl/pyridine (E) followed by aqueous KOH affords meso-F (C₆H₁₂O). Provide the structures A-F. Explain briefly.

5). Synthesis: (20 pts.) Design a synthesis of the ketone, 4-octanone, using 1-butene as your only source of carbon (4 + 4 = 8 !!!!!). All inorganic or carbon-bearing reagents are available to you. [You will most likely need some reactions from previous chapters.]

Periodic Table

Work Sheet

Work Sheet

Work Sheet