Name: Student Number: University of Manitoba - Department of Chemistry CHEM 2220 - Introductory Organic Chemistry II - Term Test 1 Thursday, February 12, 2015; 7-9 PM This is a 2-hour test, marked out of 50 points total. Part marks are available on all questions. Put all answers in the spaces provided. If more space is required you may use the backs of the exam pages but be sure to indicate that you have done so. A spectroscopic data sheet is attached at the end of the exam. QUESTION 1. Mechanism (6 Marks) 2. Mechanism (4 Marks) 3. Mechanism (4 Marks) 4. Mechanism (8 Marks) 5. Reactions and Products (22 Marks) 6. Spectra and Structures (6 Marks) TOTAL (50 Marks) MARKS
CHEM 2220 Test #1 Page 2 of 9 Feb 12, 2015 1. (6 MARKS) You have learned that epoxides will react with acids such as HBr by nucleophilic ring opening. Draw mechanisms and provide a brief explanation for the different regiochemical outcomes in the two reactions shown below.
CHEM 2220 Test #1 Page 3 of 9 Feb 12, 2015 2. (4 MARKS) 1,2,3,4,5,6-Hexachlorocyclohexane (C6H6Cl6) has many stereoisomers, including the pesticide Lindane. One of these stereoisomers undergoes E2 elimination thousands of times more slowly than the other stereoisomers under identical conditions. Identify which stereoisomer this is and briefly explain why it is so resistant to E2 elimination. 3. (4 MARKS) Normally, when 1,3-dienes react with HX species the 1,2-addition product is formed under kinetic conditions while the 1,4-addition product is thermodynamically favoured. However, when 1,4-dimethylcyclohepta-1,3-diene is treated with HBr at elevated temperature, the 1,2-product predominates rather than the 1,4-adduct! Briefly explain this result.
CHEM 2220 Test #1 Page 4 of 9 Feb 12, 2015 4. (8 MARKS) When 1,2-diols are treated with strong Brønsted acids, they can undergo the Pinacol Rearrangement. An example is shown below. Write a stepwise mechanism to explain how each of the two products is formed in this reaction. You do not have to explain the relative amounts of the products, just write the mechanism.
CHEM 2220 Test #1 Page 5 of 9 Feb 12, 2015 5. (22 MARKS) Provide the necessary reagents/solvents or starting materials or major products to correctly complete the following reactions. Mechanisms are NOT required. Show relative product stereochemistry (wedge and dash bonds) where appropriate if a racemic product is formed, simply indicate +/ or racemic. a. (2 Marks) b. (2 Marks) c. (2 Marks) d. (2 Marks) e. (2 Marks)
CHEM 2220 Test #1 Page 6 of 9 Feb 12, 2015 f. (2 Marks) g. (4 Marks) h. (6 Marks)
CHEM 2220 Test #1 Page 7 of 9 Feb 12, 2015 6. (6 MARKS Total) The IR and NMR spectra of an unknown organic compound A having the formula C6H12O are shown on the next page. Based on these data, answer the following questions about compound A. a. (1 Mark) What is the degree of unsaturation in compound A? b. (2 Marks) There are two functional groups in A. What are they? What specific spectroscopic evidence identifies each one? c. (1 Mark) In the 1 H NMR spectrum the signals between 5 ppm and 6 ppm integrate for a total of 3 hydrogens. What does this fact tell you about the structure of A? d. (1 Mark) In the 1 H NMR spectrum there is a multiplet signal between 1.3 ppm and 1.6 ppm integrating for a total of 4 hydrogens. What does this combined set of signals suggest about the structure? e. (1 Mark) What is the structure of compound A?
CHEM 2220 Test #1 Page 8 of 9 Feb 12, 2015 IR C6H12O 13 C NMR C6H12O 1 H NMR C6H12O m, 1H m, 1H m, 1H m, 1H s, 1H m, 4H tr, 3H
Page 9 of 9 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 3 0.7 1.3 C C H 2.5 3.1 C CH 2 C 1.2 1.4 C C C H C C H 1.4 1.7 O H O OH 1.5 2.5 C OH 9.5 10.0 10.0 12.0 (solvent dependent) 1.0 6.0 (solvent dependent) O 2.1 2.6 O C H 3.3 4.0 H Aryl C H 2.2 2.7 Cl C H 3.0 4.0 H 4.5 6.5 Br C H 2.5 4.0 Aryl H 6.0 9.0 I C H 2.0 4.0 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 12 11 10 9 8 7 6 5 4 3 2 1 0 Low Field 13 C NMR Typical Chemical Shift Ranges High Field Ester IR Typical Functional Group Absorption Bands CH x -Y Alkene Y = O, N Aryl Ketone, Aldehyde Amide Acid RC N 220 200 180 160 140 120 100 80 60 40 20 0 CR 3 -CH 2 -CR 3 CH x -C=O RC CR CH 3 -CR 3 Group Frequency (cm -1 ) Intensity Group Frequency (cm -1 ) Intensity C H 2960 2850 Medium RO H 3650 3400 Strong, broad C=C H 3100 3020 Medium C O 1150 1050 Strong C=C 1680 1620 Medium C=O 1780 1640 Strong C C H 3350 3300 Strong R2N H 3500 3300 Medium, broad R C C R 2260 2100 Medium (R R ) C N 1230, 1030 Medium Aryl H 3030 3000 Medium C N 2260 2210 Medium Aryl C=C 1600, 1500 Strong RNO2 1540 Strong
ANSWER KEY University of Manitoba - Department of Chemistry CHEM 2220 - Introductory Organic Chemistry II - Term Test 1 Thursday, February 12, 2015; 7-9 PM This is a 2-hour test, marked out of 50 points total. Part marks are available on all questions. Put all answers in the spaces provided. If more space is required you may use the backs of the exam pages but be sure to indicate that you have done so. A spectroscopic data sheet is attached at the end of the exam. QUESTION 1. Mechanism (6 Marks) 2. Mechanism (4 Marks) 3. Mechanism (4 Marks) 4. Mechanism (8 Marks) 5. Reactions and Products (22 Marks) 6. Spectra and Structures (6 Marks) TOTAL (50 Marks) MARKS
CHEM 2220 Test #1 Answers Page 2 of 9 Feb 12, 2015 1. (6 MARKS) You have learned that epoxides will react with acids such as HBr by nucleophilic ring opening. Draw mechanisms and provide a brief explanation for the different regiochemical outcomes in the two reactions shown below.
CHEM 2220 Test #1 Answers Page 3 of 9 Feb 12, 2015 2. (4 MARKS) 1,2,3,4,5,6-Hexachlorocyclohexane (C6H6Cl6) has many stereoisomers, including the pesticide Lindane. One of these stereoisomers undergoes E2 elimination thousands of times more slowly than the other stereoisomers under identical conditions. Identify which stereoisomer this is and briefly explain why it is so resistant to E2 elimination. 3. (4 MARKS) Normally, when 1,3-dienes react with HX species the 1,2-addition product is formed under kinetic conditions while the 1,4-addition product is thermodynamically favoured. However, when 1,4-dimethylcyclohepta-1,3-diene is treated with HBr at elevated temperature, the 1,2-product predominates rather than the 1,4-adduct! Briefly explain this result.
CHEM 2220 Test #1 Answers Page 4 of 9 Feb 12, 2015 4. (8 MARKS) When 1,2-diols are treated with strong Brønsted acids, they can undergo the Pinacol Rearrangement. An example is shown below. Write a stepwise mechanism to explain how each of the two products is formed in this reaction. You do not have to explain the relative amounts of the products, just write the mechanism. 5. The two products arise because there are two possible groups that can participate in a 1,2- shift. Note that the loss of water, the 1,2-shift and the formation of the C=O bond are probably actually more or less concerted, but they are written here as separate steps for clarity.
CHEM 2220 Test #1 Answers Page 5 of 9 Feb 12, 2015 (22 MARKS) Provide the necessary reagents/solvents or starting materials or major products to correctly complete the following reactions. Mechanisms are NOT required. Show relative product stereochemistry (wedge and dash bonds) where appropriate if a racemic product is formed, simply indicate +/ or racemic. a. (2 Marks) b. (2 Marks) c. (2 Marks) d. (2 Marks) e. (2 Marks)
CHEM 2220 Test #1 Answers Page 6 of 9 Feb 12, 2015 f. (2 Marks) 9-BBN could be used instead of BH3. B2H6 is an acceptable equivalent to BH3, as are BH3 SMe2 or BH3 THF complexes. g. (4 Marks) Note trans relationship of ester groups in Diels-Alder product requires E-alkene as dienophile. h. (6 Marks)
CHEM 2220 Test #1 Answers Page 7 of 9 Feb 12, 2015 6. (6 MARKS Total) The IR and NMR spectra of an unknown organic compound A having the formula C6H12O are shown on the next page. Based on these data, answer the following questions about compound A. a. (1 Mark) What is the degree of unsaturation in compound A? Unsaturation number is 1. b. (2 Marks) There are two functional groups in A. What are they? What specific spectroscopic evidence identifies each one? Alcohol broad IR band at ca 3400 cm -1. Alkene 13 C NMR signals at ca 113 and ca 142 ppm, and 1 H NMR signals between 5 and 6 ppm. c. (1 Mark) In the 1 H NMR spectrum the signals between 5 ppm and 6 ppm integrate for a total of 3 hydrogens. What does this fact tell you about the structure of A? There are 3 vinylic protons and only 1 alkene group so this must be a terminal alkene RCH=CH2. d. (1 Mark) In the 1 H NMR spectrum there is a multiplet signal between 1.3 ppm and 1.6 ppm integrating for a total of 4 hydrogens. What does this combined set of signals suggest about the structure? There are probably 2 CH2 groups and they are likely right next to each other since they are very similar chemical shift and show a lot of coupling. e. (1 Mark) What is the structure of compound A?
ANSWER KEY University of Manitoba - Department of Chemistry CHEM 2220 - Introductory Organic Chemistry II - Term Test 1 Thursday, February 12, 2015; 7-9 PM This is a 2-hour test, marked out of 50 points total. Part marks are available on all questions. Put all answers in the spaces provided. If more space is required you may use the backs of the exam pages but be sure to indicate that you have done so. A spectroscopic data sheet is attached at the end of the exam. QUESTION 1. Mechanism (6 Marks) 2. Mechanism (4 Marks) 3. Mechanism (4 Marks) 4. Mechanism (8 Marks) 5. Reactions and Products (22 Marks) 6. Spectra and Structures (6 Marks) TOTAL (50 Marks) MARKS
CHEM 2220 Test #1 Answers Page 2 of 9 Feb 12, 2015 1. (6 MARKS) You have learned that epoxides will react with acids such as HBr by nucleophilic ring opening. Draw mechanisms and provide a brief explanation for the different regiochemical outcomes in the two reactions shown below.
CHEM 2220 Test #1 Answers Page 3 of 9 Feb 12, 2015 2. (4 MARKS) 1,2,3,4,5,6-Hexachlorocyclohexane (C6H6Cl6) has many stereoisomers, including the pesticide Lindane. One of these stereoisomers undergoes E2 elimination thousands of times more slowly than the other stereoisomers under identical conditions. Identify which stereoisomer this is and briefly explain why it is so resistant to E2 elimination. 3. (4 MARKS) Normally, when 1,3-dienes react with HX species the 1,2-addition product is formed under kinetic conditions while the 1,4-addition product is thermodynamically favoured. However, when 1,4-dimethylcyclohepta-1,3-diene is treated with HBr at elevated temperature, the 1,2-product predominates rather than the 1,4-adduct! Briefly explain this result.
CHEM 2220 Test #1 Answers Page 4 of 9 Feb 12, 2015 4. (8 MARKS) When 1,2-diols are treated with strong Brønsted acids, they can undergo the Pinacol Rearrangement. An example is shown below. Write a stepwise mechanism to explain how each of the two products is formed in this reaction. You do not have to explain the relative amounts of the products, just write the mechanism. 5. The two products arise because there are two possible groups that can participate in a 1,2- shift. Note that the loss of water, the 1,2-shift and the formation of the C=O bond are probably actually more or less concerted, but they are written here as separate steps for clarity.
CHEM 2220 Test #1 Answers Page 5 of 9 Feb 12, 2015 (22 MARKS) Provide the necessary reagents/solvents or starting materials or major products to correctly complete the following reactions. Mechanisms are NOT required. Show relative product stereochemistry (wedge and dash bonds) where appropriate if a racemic product is formed, simply indicate +/ or racemic. a. (2 Marks) b. (2 Marks) c. (2 Marks) d. (2 Marks) e. (2 Marks)
CHEM 2220 Test #1 Answers Page 6 of 9 Feb 12, 2015 f. (2 Marks) 9-BBN could be used instead of BH3. B2H6 is an acceptable equivalent to BH3, as are BH3 SMe2 or BH3 THF complexes. g. (4 Marks) Note trans relationship of ester groups in Diels-Alder product requires E-alkene as dienophile. h. (6 Marks)
CHEM 2220 Test #1 Answers Page 7 of 9 Feb 12, 2015 6. (6 MARKS Total) The IR and NMR spectra of an unknown organic compound A having the formula C6H12O are shown on the next page. Based on these data, answer the following questions about compound A. a. (1 Mark) What is the degree of unsaturation in compound A? Unsaturation number is 1. b. (2 Marks) There are two functional groups in A. What are they? What specific spectroscopic evidence identifies each one? Alcohol broad IR band at ca 3400 cm -1. Alkene 13 C NMR signals at ca 113 and ca 142 ppm, and 1 H NMR signals between 5 and 6 ppm. c. (1 Mark) In the 1 H NMR spectrum the signals between 5 ppm and 6 ppm integrate for a total of 3 hydrogens. What does this fact tell you about the structure of A? There are 3 vinylic protons and only 1 alkene group so this must be a terminal alkene RCH=CH2. d. (1 Mark) In the 1 H NMR spectrum there is a multiplet signal between 1.3 ppm and 1.6 ppm integrating for a total of 4 hydrogens. What does this combined set of signals suggest about the structure? There are probably 2 CH2 groups and they are likely right next to each other since they are very similar chemical shift and show a lot of coupling. e. (1 Mark) What is the structure of compound A?
CHEM 2220 Test #1 Answers Page 8 of 9 Feb 12, 2015 IR C6H12O 13 C NMR C6H12O 1 H NMR C6H12O m, 1H m, 1H m, 1H m, 1H s, 1H m, 4H tr, 3H
Page 9 of 9 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 3 0.7 1.3 C C H 2.5 3.1 C CH 2 C 1.2 1.4 C C C H C C H 1.4 1.7 O H O OH 1.5 2.5 C OH 9.5 10.0 10.0 12.0 (solvent dependent) 1.0 6.0 (solvent dependent) O 2.1 2.6 O C H 3.3 4.0 H Aryl C H 2.2 2.7 Cl C H 3.0 4.0 H 4.5 6.5 Br C H 2.5 4.0 Aryl H 6.0 9.0 I C H 2.0 4.0 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 12 11 10 9 8 7 6 5 4 3 2 1 0 Low Field 13 C NMR Typical Chemical Shift Ranges High Field Ester IR Typical Functional Group Absorption Bands CH x -Y Alkene Y = O, N Aryl Ketone, Aldehyde Amide Acid RC N 220 200 180 160 140 120 100 80 60 40 20 0 CR 3 -CH 2 -CR 3 CH x -C=O RC CR CH 3 -CR 3 Group Frequency (cm -1 ) Intensity Group Frequency (cm -1 ) Intensity C H 2960 2850 Medium RO H 3650 3400 Strong, broad C=C H 3100 3020 Medium C O 1150 1050 Strong C=C 1680 1620 Medium C=O 1780 1640 Strong C C H 3350 3300 Strong R2N H 3500 3300 Medium, broad R C C R 2260 2100 Medium (R R ) C N 1230, 1030 Medium Aryl H 3030 3000 Medium C N 2260 2210 Medium Aryl C=C 1600, 1500 Strong RNO2 1540 Strong