EXAM 3

CHEMISTRY 220

Friday, November 12, 2010

NAME (print): ________________________________________________________

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

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

No calculators or electronic devices. You may use molecular models. Important clues and structures are in bold. There is a Periodic Table on page 8.

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. (15 pts) Structure Determination ______

2. (30 pts) Reactions (Do 5 of 6) ______

3. (25 pts) Potpourri (Do 5 of 6) ______

4. (30 pts) Mechanism ______

____________________________________________________

Total (100 pts)

1) Structure Determination: (15 pts.) Optically-active compound A (C10H16) [Degrees of Unsaturation?] reacts with Pt/H2 to afford optically-active compound B (C10H20) [Degrees of Unsaturation?]. Ozonolysis of A followed by dimethyl sulfide reduction provides a single compound (S)-1. Draw (S)-1. What are the structures of A and B? Explain your reasoning.

2) Reactions: (5 x 6 pts. = 30 pts.) Complete 5 of 6 of the following questions by providing structures, reagents, etc. Pay attention to stereochemistry, etc. Several steps may be required. If you do more than 5 questions, clearly cross out the answer you do not want graded.

…continued

3) Potpourri: (5 x 5 pts. = 25 pts.) Provide the missing information in 5 of 6 of the following questions. If you do more than 5 questions, clearly cross out the answer you do not want graded.

a) Circle the terms that best apply to the hydration of 3-decyne with HgSO₄/aq. H₂SO₄.

regioselective stoichiometric Hg⁺⁺ oxidation reduction enol tautomerization

b) Circle the heptene with the greater heat of hydrogenation.

c) Circle the compound(s) with a degree of unsaturation = 9.

C₁₇H₂₁NO₄ C₁₇H₁₉NO₃ C₁₇H₁₇Cl₂N

(cocaine) (morphine) (Sertraline – Zoloft)

d) Circle the terms that apply to the reaction of OsO₄/H₂O₂ with (E)-3-hexene.

catalytic regioselective d,l-pair reduction optically-active

e) Estimate the heat of formation of 5-decyne given that DH_f^o = +34.8 kcal/mol for 2-butyne. Show work.

f) Write a brief description of the relevance of the work of Paul Sabatier (Nobel Prize 1912) to the chemistry covered on this exam.

4) Mechanisms: (5 x 5 pts. = 25 pts.) Complete each of the questions below.

On Hydroboration:

i) Hydroboration is said to be an anti-Markovnikov addition of water to a trisubstituted alkene. What critical mechanistic issue is missing from the previous sentence? Think mechanism.

ii) The hydroboration step is a Markovnikov addition of borane to an alkene. It is also a reduction. Explain.

iii) In the second step of a hydroboration reaction, what is the reagent and what special mechanistic feature is observed.

…continued

iv) In the reaction of a terminal alkyne in a typical hydroboration procedure, why is diisoamylborane employed rather than borane? What is the downside?

v) For the preparation of secondary alcohols the hydroboration of the stereoisomers of 3-hexene is an acceptable procedure. The same cannot be said for the 2-hexenes. Explain.

Work Sheets
Work Sheets
Work Sheets