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Presentation/PPT
27/08/2022
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Your Name:
Isomer Relationships, Conformational Stability, and Reaction Selectivity
Instructions:
Read the instructions carefully and answer the following questions in the space provided. Then
attach the PDF file on Discussion Board for peer discussion and peer review.
1. In a few sentences define each of the three main classes of isomers below. Configurational
Isomers can be further classified as either enantiomers or diastereomers and should also be
discussed. Your descriptions should enable your peers to quickly and easily compare and
contrast the differences between the different classes of isomers.
A. Constitutional Isomers (or Structural Isomers)
B. Conformational Isomers
C. Configurational Isomers (or Stereoisomers)
I. Enantiomers
II. Diastereomers
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2. Analyze each pair of compounds below. Identify which class of isomers each pair of
structures represent. Your choices are: (i) constitutional, (ii) conformational, (iii)
enantiomers, or (iv) diastereomers or (v) identical (non-isomers). Only one label for each
pair should be used. For each case show work (drawings, (R)/(S), rotation of bonds, chair-
flips, etc) which led you to each answer for the pairs below. [During your peer review, any
differences of answers between you and your peers can be discussed and corrected as
needed.]
Note: Various projections may be used when drawing chemical structures including bond-
line structures (using proper dash/wedge bonds), Newman projections, chair structures (for
cyclohexane derivatives), Haworth projections, and Fischer projections. These projections
just represent different vantage points of visualizing a chemical structure and can be
interconverted from one projection to another. Each different projection has been labeled
for you below. These are all utilized throughout the text book.
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3. Analyze the structures for Compound A and Compound B shown below. Answer and
discuss each question (a) and (b), respectively.
a. What type of isomers do these represent?
b. Which compound is more stable? (Hint: You will need to draw the chair structures
for each compound (4 total chairs, two for each compound) and
compare/contrast/analyze the various 1,3-diaxial interactions in order to justify this
answer. Show your work clearly.
O
O
CH3 O
O
CH3
Compound A Compound B
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4. Chiral catalysts can be designed to favor the formation of one enantiomer over another in
reactions where a new chiral center is formed. The example shown below was recently
reported in the chemical literature (J. Am. Chem. Soc. 2012, 134, 8054–8057) where a new
type of chiral copper (Cu) catalyst was developed. When the CuI catalyst was used, the
(S)-enantiomer of the product predominated, and the (R)-enantiomer of the product was
selectively formed when CuII catalyst was used instead.
Answer part (a) and (b) below. You aren’t required to understand the chemistry to
answer correctly and discuss the experimental results.
a. The product has been shown on the right of the reaction scheme above but the absolute
stereochemistry of the product has been excluded. Draw the major enantiomer formed
when each form of the catalyst is used. You need to be sure to show the stereochemistry
clearly using appropriate dash/wedge bonds at the stereocenter and indicate which catalyst
(CuI or CuII) was used for each of the two individual enantiomers you draw.
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b. The chart below reports the data when the (S)-selective catalyst was used in various
solvents. The enantiomeric excess (reported as % ee ) is shown for each case.
Complete the table above by calculating the % (S) and % (R) formed when the (S)-selective
reaction was repeated in the various solvents. How are these values calculated? Illustrate this by
showing a complete calculation for the toluene case. For the others, you can simply just write in
the values. If your values do not match your peers’, you will need to discuss this and correct as
needed. Also, discuss which solvent gives the optimal results in terms of both enantioselectivity
and overall total product yield. What experimental data led you to make this conclusion? Where
any other solvents comparable? What solvent gave the worst results?
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