CHM 2120C - Final exam PDF

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Summary

Final exam for organic chem II over the summer...

Description

Faculté des Sciences | Faculty of Science Département de chimie et science biomoléculaire | Department of Chemistry and Biomolecular Sciences Pavillon STEM building (342) 150 Louis Pasteur Pvt Ottawa ON Canada  613-562-5728  613-562-5193

K1N 6N5 [email protected]

Final Exam - CHM 2120C Date: August 20, 2021

Length: 3 h

Professor: Claudia El Nachef

Last Name: _______________________

First Name: ________________________

Student # _________________________

Instructions: - This is a closed book exam. - Faculty-approved calculator is allowed. - Molecular model is permitted. - The last two pages contain a periodic table, a simplified pKa table, an approximate IR wavenumber and 1H NMR approximate chemical shifts tables. - Total number of pages: 13 - Total number of points is 106 Please read carefully: Cellular phones, unauthorized electronic devices or course notes (unless an open-book exam) are not allowed during this exam. Except for thePhones and devices must be turned off and put away in your bag. Do not keep them in your possession, such as in your pockets. If caught with such a device or document, the following may occur: academic fraud allegations will be filed which may result in your obtaining a 0 (zero) for the exam. By signing below, you acknowledge that you have read and ensured that you are complying with the above statement.

Signature: ________________________________

GOOD LUCK! 1/13

1. Rank the following molecules in decreasing order of reactivity with CH3MgBr (from the most reactive to the least reactive). (2 points)

________ > _________ > _________ > __________> __________

2. Identify the most electrophilic molecule (A or B) in each of the following pairs? (3 points)

3. Using resonance forms, explain briefly your choice for the previous question "2-ii". (2 points)

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4. Which nitrogen in this molecule is the most basic? Explain briefly your choice. (2 points)

5. If the following molecule was treated with one molar equivalent of NaOH, which proton would predominantly be removed? Explain briefly your choice. (2 points)

6. The IR and the 1H NMR spectra of an unknown with a molecular formula of C8H14O2 are shown below. The questions that follow will guide you in the determination of its structure.

a. Determine the degree of unsaturation. Show your calculation. (1.5 points)

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b. Analyze three significant bands in the IR spectra and conclude on the existing functions. (3 points)

c. Analyze the 1H NMR spectral data in the table below. (3.5 points) δ (ppm)

Integra -tion

Multiplicity

0.90

3H

t

1.50-1.60

2H

m

1.65-1.75

2H

m

2.05

3H

s

E

4.10

2H

t

F

5.50

1H

d

G

6.10

1H

d

Signal

A B C D

Comments

d. Draw the final structure of the unknown in this box below. (3 points)

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7. For each of the following reactions, Identify the orbital that represents the highest occupied molecular orbital (HOMO) and the one that represents the lowest unoccupied molecular orbital (LUMO). (4 points) a)

b)

8. The following reactions will not work as shown. Explain why by showing the reaction that would occur instead. (4 points)

9. Compound A was heated with methanol B to give product C. The reaction rate observed was 2.5 x 10-4 M.s-1 when the concentrations of A and B were 0.1 M and 0.2 M respectively. 5/13

a) Show the reaction mechanism and draw the product C in the box above. (3 points)

Free Energy

b) Draw the energy diagram of the reaction. Please clearly draw the transition state of the rate-determining step: (4 points)

Reaction Coordinate c) Now that you have identified how the reaction is proceeding, determine the rate of this reaction when the concentration of A is 0.3 M and of B is 0.4 M. Show your work. (3 points)

10. Outline two Wittig alkene syntheses of 2,3-dimethyl-1-butene. Is one synthesis preferred over the other? If yes, please indicate which one and your reasoning. No need to show the mechanism, only reactants. (6 points) 6/13

11. a. Draw the kinetic and thermodynamic enolates of the ketone below: (4 points)

b. On the reaction coordinate diagram, identify which enolate fits in each empty box.

E

A Reaction coordinate 12. Complete each of these following reactions (i.e. fill in the boxes with the missing reagent(s) or major product(s). (24 points)

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13. Provide a detailed mechanism for the following reactions and determine the product: (20 points)

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14. Provide a synthesis to form these products from the starting materials shown and any other necessary reactants and reagents. (12 points)

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Unofficial final marks will be posted on Brightspace as soon as they are available.

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Table of approximate chemical shifts of most protons

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