EXAM 3

CHEMISTRY 225b

Friday, April 25, 2008

NAME (print): ___________________________________________________

TA:_____________________ Day:_________________ Time:__________

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

Important clues, points, and structures are in bold.

Do all preliminary drawing or computations on the work sheets at the end of the exam. The work sheets will not be graded

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. (30 pts) Reactions ______

2. (30 pts) Potpourri ______

3. (20 pts) Synthesis ______

4. (20 pts) Structure ______

_____________________________________

Total (100 pts)

1. (30 pts) Reactions: Provide answers to the following reactions.

2. (30 pts.) Potpourri: Complete each of the following questions.

a) Stable solutions of the lithium salt of 1-octyne can be prepared in which of the following solvents (Circle your answer(s)).

(E)-3-hexene H₂O acetone NH₃ (CH₃)₃COH

b) Lindlar reduction of 2-pentyne liberates 37.4 kcal/mol of heat. Hydrogenation of (E)-2-pentene liberates 27.4 kcal/mol of heat to form n-pentane (DH_f^o=-35.1 kcal/mol). Circle your best estimate for the heat of formation of 2-pentyne (kcal/mol)? (What do you know about the DH_f^o of (E)- and (Z)-disubstituted alkenes?)

-29.7 -30.7 +29.7 +30.7 -7.7

c) Circle the halide(s) that will form viable Grignard reagents.

BrCH₂CH₂Br HOCH₂CH₂CH₂Br CH₃CH₂OCH₂CH₂CH₂Cl

BrCH₂CH₂CHO BrCH₂CH₂CO₂H

d) Circle the greatest number of compounds that are at the same oxidation level.

e) Circle the products expected to be formed during the hydrolysis of methyl benzoate with H₃¹⁸O⁺.

3. (20 pts) Synthesis: Design a synthesis of (±)-epoxide 1 using 2-butyne as your only source of carbon. All other reagents are available to you. [Hint: You did most of this problem on your homework.]

4. (20 pts). Structure: Optically-active alkyne A, C₁₀H₁₈, undergoes reduction to form compound B (C₁₀H₂₀). Compounds A or B form a single (S)-carboxylic acid (C₅H₁₀O₂) C upon oxidation with aqueous KMnO₄. [At this point you should know the structures of A and C and some of B]. Compound B also reacts with bromine to form two (and not one) optically active dibromides D and E (D and E are not distinguishable). What are the structures of A-E? Show how D and E determine the stereochemical issue in B. How was A reduced to B?
Work Sheets
Work Sheets
Work Sheets