CHEM 2220 Organic Chemistry II: Reactivity and Synthesis Prof. P.G. Hultin. FINAL EXAM Winter Session 2017R

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1 CHEM 2220 Organic Chemistry II: Reactivity and Synthesis Prof. P.G. Hultin FINAL EXAM Winter Session 2017R Tuesday April 25, :00 am 11:00 am Frank Kennedy Gold Gym PRINT LEGIBLY PLEASE Name: Student Number: This is a closed-book time-limited invigilated exam. Students are permitted to bring into the exam room ONE SHEET of LETTER-SIZE (8½ x 11 inches) paper with any HANDWRITTEN notes they wish (both sides). Molecular model kits, rulers and calculators are permitted but no other aids may be used. The exam is divided into 5 parts, with total marks as noted below. All answers are to be written in the spaces provided in this stapled package. Submit this package when you are finished writing the exam. Please do not put your name or student number on individual pages of this package. Only put identification on this title page. The separate spectroscopy page will not be handed in and you should not write answers there. Part 1 Reactions and Products Part 2 Synthesis Part 3 Mechanism Part 4 Mechanism pot-pourri Part 5 Spectroscopy TOTAL: (40 Marks) (15 Marks) (14 Marks) (24 Marks) (7 Marks) (100 Marks) Page 1 of 10

2 1. (40 MARKS) Reactions and Products. Supply the missing molecular structure or reagent/solvent/reaction conditions to correctly complete the following reactions. Show stereochemistry when necessary. If a compound is racemic, indicate this by writing racemic or +/-. Simple aqueous acid or base workups can be assumed but any special workup conditions should be specified. (a) (b) (c) (d) (e) Page 2 of 10

3 (f) (4 Marks) (g) (h) (i) (j) Page 3 of 10

4 (k) (4 Marks) (l) (4 Marks) (m) (4 Marks) (n) (o) (4 Marks) Page 4 of 10

5 2. (15 MARKS) Propose a practical synthetic route to prepare 2-chromanone starting from phenol. You may use any other reagent or solvent needed. There are at least 2 routes based on reactions covered in CHEM 2220 that require fewer than SIX steps. (a) (5 Marks) Give a stepwise retrosynthetic analysis describing your route. Remember to use the correct retrosynthetic arrows for each disconnection step in your analysis. (b) (10 Marks) Re-write your route in the forward synthetic direction. For each step, provide the specific reagents and conditions and the structure of the product formed. Page 5 of 10

6 3. (14 MARKS TOTAL) The following reaction was a key step in a synthesis of a cytotoxic alkaloid called Crispine A published in The researchers noted that the intermediate X was formed very rapidly at room temperature, and it could be observed by NMR in the reaction mixture. The spectra clearly showed that compound X contained an RCH 2Cl group. Intermediate X was converted more slowly into the final product. (a) Identify the most nucleophilic atom in the reactants. (b) An acetal can be hydrolyzed by aqueous acid. There is no water in this reaction, but there is an acid present! Use these facts to write an arrow-pushing mechanism showing how an electrophilic site is created from the acetal reactant. (c) Number the carbon atoms in the acetal reactant and then apply the same numbers to the corresponding atoms in the product structure. (The atoms from the amino-ester should be obvious). Part d of this question is on the next page of this exam! Page 6 of 10

7 (d) (8 Marks) Use the information you now have to write a mechanism for the overall reaction, and identify intermediate X in your mechanism. Page 7 of 10

8 4. (24 MARKS TOTAL) Mechanism pot-pourri! Assorted shorter mechanisms from across the course. (a) (8 Marks) The beauty of pericyclic reactions is their ability to achieve enormous structural changes with exquisite stereochemical control. Provide mechanisms for the two transformations of compound A shown below. Identify the type of reaction, how many pi electrons are involved and whether the processes are conrotatory or disrotatory. (b) (6 Marks) When the α,β-unsaturated ketone shown was boiled in the presence of polyphosphoric acid, 3-phenyl-1-indanone was obtained in moderate yield. Provide a stepwise mechanism for this transformation. You can represent polyphosphoric acid by H +. Page 8 of 10

9 (c) (4 Marks) Di-iodination of alkenes and alkynes is not usually a thermodynamically favourable reaction, but this interesting process was extremely efficient, giving the product in 94% isolated yield. Taking into account the fact that sp 2 cations are very high-energy intermediates, write a plausible mechanism to explain this process. (d) (6 Marks) Provide a plausible reaction mechanism for the following reaction. Notice the stereochemical relationships between the starting material and the product. Page 9 of 10

10 5. (7 MARKS Total) Spectroscopy. The molecular formula of an unknown organic compound is C 9H 7NO 3. The IR, 13 C NMR and 1 H NMR spectra of this compound are attached to the exam. Answer the following questions about this compound based on these spectra. (a) (1 Mark) What is the unsaturation number for this compound? (b) (1 Mark) What functional group contains the nitrogen atom, and what spectroscopic evidence supports your conclusion? (c) What specific functional group gives rise to the 13 C NMR signal at 192 ppm? What other spectroscopic evidence supports your conclusion? (d) (1 Mark) There are two doublets each integrating for 2H in the 1 H NMR spectrum at 8.31 and 7.76 ppm. What structural conclusion can be drawn from these? (e) (1 Mark) What do the two 1 H signals at 7.57 and 6.83 ppm tell us about the structure? Explain their J-coupling. (f) (1 Mark) Draw the structure of this compound in the box below. Structure for C 9H 7NO 3 Page 10 of 10

11 CHEM 2220 Final 2017R THIS PAGE NOT TO BE HANDED IN Page 1 of 2 Spectra for Part 5 IR C9H7NO3 13 C NMR C9H7NO3 NB: solvent peaks have been edited out. 1 H NMR C9H7NO3 J = 7.5 Hz J = 16.2 Hz J = 16.2 Hz and 7.5 Hz 1H d 2H d 2H d 1H d 1H dd

12 THIS PAGE NOT TO BE HANDED IN Page 2 of 2 Spectroscopy Crib Sheet for CHEM 2220 Introductory Organic Chemistry II 1 H NMR Typical Chemical Shift Ranges Type of Proton Chemical Shift (δ) Type of Proton Chemical Shift (δ) C CH C C H C CH 2 C C C C H C C H O H O OH C OH (solvent dependent) (solvent dependent) O O C H H Aryl C H Cl C H H Br C H Aryl H I C H RCO 2 H Aromatic, heteroaromatic X C H X = O, N, S, halide R 3 C H Aliphatic, alicyclic Y = O, NR, S Y H H Y H Y = O, NR, S Low Field High Field 13 C NMR Typical Chemical Shift Ranges Ketone, Aldehyde Ester Acid Amide Alkene Aryl RC N CH x -Y: Y = O, N CR 3 -CH 2 -CR 3 CH x -C=O RC CR CH 3 -CR IR Typical Functional Group Absorption Bands Group Frequency Frequency (cm -1 Intensity Group ) (cm -1 ) Intensity C H Medium RO H Strong, broad C=C H Medium C O Strong C=C Medium C=O Strong C C H Strong R2N H Medium, broad R C C R Medium (R R ) C N 1230, 1030 Medium Aryl H Medium C N Medium Aryl C=C 1600, 1500 Strong RNO Strong

13 CHEM 2220 Organic Chemistry II: Reactivity and Synthesis Prof. P.G. Hultin FINAL EXAM Winter Session 2017R Tuesday April 25, :00 am 11:00 am Frank Kennedy Gold Gym PRINT LEGIBLY PLEASE Name: ANSWER KEY Student Number: This is a closed-book time-limited invigilated exam. Students are permitted to bring into the exam room ONE SHEET of LETTER-SIZE (8½ x 11 inches) paper with any HANDWRITTEN notes they wish (both sides). Molecular model kits, rulers and calculators are permitted but no other aids may be used. The exam is divided into 5 parts, with total marks as noted below. All answers are to be written in the spaces provided in this stapled package. Submit this package when you are finished writing the exam. Please do not put your name or student number on individual pages of this package. Only put identification on this title page. The separate spectroscopy page will not be handed in and you should not write answers there. Part 1 Reactions and Products Part 2 Synthesis Part 3 Mechanism Part 4 Mechanism pot-pourri Part 5 Spectroscopy TOTAL: (40 Marks) (15 Marks) (14 Marks) (24 Marks) (7 Marks) (100 Marks) Page 1 of 10

14 1. (40 MARKS) Reactions and Products. Supply the missing molecular structure or reagent/solvent/reaction conditions to correctly complete the following reactions. Show stereochemistry when necessary. If a compound is racemic, indicate this by writing racemic or +/-. Simple aqueous acid or base workups can be assumed but any special workup conditions should be specified. (a) (b) (c) (d) (e) Page 2 of 10

15 (f) (4 Marks) (g) (h) (i) (j) Page 3 of 10

16 (k) (4 Marks) (l) (4 Marks) (m) (4 Marks) (n) (o) (4 Marks) Page 4 of 10

17 2. (15 MARKS) Propose a practical synthetic route to prepare 2-chromanone starting from phenol. You may use any other reagent or solvent needed. There are at least 2 routes based on reactions covered in CHEM 2220 that require fewer than SIX steps. (a) (5 Marks) Give a stepwise retrosynthetic analysis describing your route. Remember to use the correct retrosynthetic arrows for each disconnection step in your analysis. (b) (10 Marks) Re-write your route in the forward synthetic direction. For each step, provide the specific reagents and conditions and the structure of the product formed. Several variations in reagents are possible, and we can t really tabulate every single one. Any chemistry that works gets marks. Likewise, there are probably other retrosynthetic analyses that can be devised, which would lead to different syntheses. If the chemistry is ok, there is no problem. Page 5 of 10

18 3. (14 MARKS TOTAL) The following reaction was a key step in a synthesis of a cytotoxic alkaloid called Crispine A published in The researchers noted that the intermediate X was formed very rapidly at room temperature, and it could be observed by NMR in the reaction mixture. The spectra clearly showed that compound X contained an RCH 2Cl group. Intermediate X was converted more slowly into the final product. (a) Identify the most nucleophilic atom in the reactants. The amine nitrogen in the amino acid is the most nucleophilic. (b) An acetal can be hydrolyzed by aqueous acid. There is no water in this reaction, but there is an acid present! Use these facts to write an arrow-pushing mechanism showing how an electrophilic site is created from the acetal reactant. (c) Number the carbon atoms in the acetal reactant and then apply the same numbers to the corresponding atoms in the product structure. (The atoms from the amino-ester should be obvious). Part d of this question is on the next page of this exam! Page 6 of 10

19 (d) (8 Marks) Use the information you now have to write a mechanism for the overall reaction, and identify intermediate X in your mechanism. Page 7 of 10

20 4. (24 MARKS TOTAL) Mechanism pot-pourri! Assorted shorter mechanisms from across the course. (a) (8 Marks) The beauty of pericyclic reactions is their ability to achieve enormous structural changes with exquisite stereochemical control. Provide mechanisms for the two transformations of compound A shown below. Identify the type of reaction, how many pi electrons are involved and whether the processes are conrotatory or disrotatory. (b) (6 Marks) When the α,β-unsaturated ketone shown was boiled in the presence of polyphosphoric acid, 3-phenyl-1-indanone was obtained in moderate yield. Provide a stepwise mechanism for this transformation. You can represent polyphosphoric acid by H +. Protonating the C=C bond directly will also form a carbocation at the required location, but 1) the oxygen is more basic, and 2) the cation is more delocalized hence likely lower in energy. Page 8 of 10

21 (c) (4 Marks) Di-iodination of alkenes and alkynes is not usually a thermodynamically favourable reaction, but this interesting process was extremely efficient, giving the product in 94% isolated yield. Taking into account the fact that sp 2 cations are very high-energy intermediates, write a plausible mechanism to explain this process. (d) (6 Marks) Provide a plausible reaction mechanism for the following reaction. Notice the stereochemical relationships between the starting material and the product. Page 9 of 10

22 5. (7 MARKS Total) Spectroscopy. The molecular formula of an unknown organic compound is C 9H 7NO 3. The IR, 13 C NMR and 1 H NMR spectra of this compound are attached to the exam. Answer the following questions about this compound based on these spectra. (a) (1 Mark) What is the unsaturation number for this compound? Unsaturation = 7 (b) (1 Mark) What functional group contains the nitrogen atom, and what spectroscopic evidence supports your conclusion? Probably NO2 IR band at ~1550, no evidence of N-H in IR or 1 H NMR. (c) What specific functional group gives rise to the 13 C NMR signal at 192 ppm? What other spectroscopic evidence supports your conclusion? (d) (1 Mark) There are two doublets each integrating for 2H in the 1 H NMR spectrum at 8.31 and 7.76 ppm. What structural conclusion can be drawn from these? (e) (1 Mark) What do the two 1 H signals at 7.57 and 6.83 ppm tell us about the structure? Explain their J-coupling. (f) (1 Mark) Draw the structure of this compound in the box below. Structure for C 9H 7NO 3 Page 10 of 10

Name: Student Number: University of Manitoba - Department of Chemistry CHEM Introductory Organic Chemistry II - Term Test 2

Name: Student Number: University of Manitoba - Department of Chemistry CHEM 2220 - Introductory Organic Chemistry II - Term Test 2 Thursday, March 12, 2015; 7-9 PM This is a 2-hour test, marked out of