CH 250 Block 3 2012
Exam #2 (100 points)
Name:
Date:
Honor Code:
“Dans les champs de l'observation le hasard ne favorise que les esprits préparés.”
“In the fields of observation chance favors only the prepared mind.” Louis Pasteur, Lecture,
University of Lille (7 December 1854)
The Rules: You have until noon to complete the exam unless you have provided me with documentation for
extra time. When you are done with your exam, please place it in the box outside my office. In fairness to all,
anyone who turns in an exam late will receive a grade of zero!
You may use your model kits. A periodic table, pKa table, IR table, and 1H NMR table are provided as a
supplementary packet. No notes or textbook allowed. This exam is an individual assessment—no teamwork,
paid consultants, etc.
You may take the exam in Olin 1 or the Olin fishbowl.
Be sure to read the instructions for each question. It may be helpful to skim the entire exam and solve the
easier questions first.
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1) (12 points)
a) Draw the substitution product and the MAJOR elimination product for the reaction below. Show any
relevant stereochemistry.
b) Choose either the substitution reaction or the elimination reaction from part a. Draw a detailed
transition state that explains the product structure.
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2) (14 points)
Pat, a junior chemist at MakeABuck Pharma, has been assigned the unfortunate and smelly task of
preparing the following sulfur-containing drug precursors. Things are off to a rough start for Pat. Pat
has been asked to prepare the product shown (B) from alkyl halide A, and chose to use the conditions
shown below. Unfortunately, but not surprisingly, Pat obtained a mixture of two products-- his
desired product and an undesired isomer (1: 1 ratio) .
(a) Draw the undesired isomer obtained in this reaction. Is this an enantiomer, diastereomer, or
constitutional isomer of B?
(b) Draw a detailed mechanism and any key intermediate structures that explain why two products
were observed in Pat’s first attempt.
(c) Suggest alternate reaction conditions that would be more likely to give the desired product without
formation of an isomer. (You must still use the same starting alkyl halide A).
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3) (10 points) The following month, Pat’s new replacement, Jamie, is preparing another drug precursor.
Jamie is considering two possible protocols for the preparation of the iodoalkane product shown
below.
a) Which protocol do you recommend? Explain your rationale.
b) Give the IUPAC name for the product.
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4) (18 points)
a) Draw a detailed mechanism to explain the outcome of the substitution reaction above. Be sure to
show all bond breaking and bond forming steps and show all intermediates.
b) Draw an energy diagram that correlates to the mechanism for part a. Draw the structures of any
intermediates on your energy diagram.
c) Draw the most significant elimination product that you might expect to find under these reaction
conditions.
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5) (12 points) A compound with molecular formula C4H6O4 produces a 1H NMR spectrum with two
signals—a singlet at 12.1 ppm with relative integration of 1 and a singlet at 2.4 ppm with a relative
integration of 2. The IR spectrum produces a broad signal between 2500 and 3600 cm-1.
a) Deduce the structure of the compound.
b) Note on your structure which groups correspond to each signal in the data sets above.
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6) (18 points) A distracted chemist was rounding up 5 solvent bottles for a series of experiments, but
forgot to label the bottles. He now must use his IR and NMR know-how to determine which bottle is
which. The following 5 solvents were in his collection:
Methanol (CH3OH)
Isopropanol (CH3)2CHOH
Ethanol (CH3CH2OH)
Ethyl acetate (CH3CO2CH2CH3)
Benzene (aromatic ring) (C6H6)
a) He was fairly confident in identifying two solvents simply by looking at the IR spectra. Match the IR
spectra to the appropriate solvents. Label any diagnostic peaks.
IR Spectrum #1:
IR Spectrum #2:
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b) He was able to more confidently assign the structures using 1H NMR. Label each spectrum below with
the corresponding structure and assign all of the peaks in the spectra (e.g. label which protons on the
structure correspond to each signal in the spectrum.)
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c) Classify each of the following solvents as “polar protic” or “polar aprotic.” Which solvents are preferred
for SN1 reactions? Which solvents are preferred for SN2 reactions?
Methanol (CH3OH):
Isopropanol (CH3)2CHOH:
Ethanol (CH3CH2OH):
Ethyl acetate (CH3CO2CH2CH3):
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7) (16 points) Propose a synthesis of the following compounds. Show the starting material, reagents, and solvents
you would use. Note whether your proposed reaction is an SN1, SN2, E1, or E2 reaction and explain your answer.
(a)
(b)
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