CHEM 39, Spring 2007
News and Updates:
Gradelines for Chem 39, Spring 2007 (Peterson; updated 5/9/07):
The following minimum average scores are required:
A 87
A- 81
B+ 76
B 71
B- 66
C+ 57
C 52
D 37
Monday, May 7, 2007
The average for the final was 59%. Here are the correct answers for the final exam:
Question #, Form A, Form B
1, B, I
2, C, A
3, C, B
4, B, G
5, B, J
6, D, B
7, C, G
8, I, A
9, J, E
10, G, B
11, G, J
12, A, B
13, E, D
14, B, C
15, J, I
16, B, J
17, E, G
18, C, B
19, I, B
20, A, C
21, B, C
22, G, B
23, J, B
24, B, E
25, B, C
Friday, May 4, 2007 (Lecture 42)
Today, we finished discussing pericyclic reactions by discussing how to predict the regiochemistry and stereochemistry of Diels Alder reactions.Good luck on the final exam!
Wednesday, May 2, 2007 (Lecture 41)
Johannes lead a review session in class today.
Monday, April 30, 2007 (Lecture 40)
Today, we started pericyclic reactions, which includes parts of chapters 14 and 30. We introduced three classes of pericyclic reactions and had a brief review of molecular orbital theory.
Friday, April 27, 2007 (Lecture 39)
We talked about DNA sequencing and solid-phase DNA synthesis.
Wednesday, April 15, 2007 (Lecture 38)
We continued to talk about Chapter 28 on Heterocycles and Nucleic Acids. The structure of DNA, base pairing and hydrogen bonding between bases, and DNA replication were discussed.We talked about DNA sequencing and briefly discussed DNA synthesis.
Monday, April 23, 2007 (Lecture 37)
We started Chapter 28 on Heterocycles and Nucleic Acids. DNA and RNA were introduced today. We discussed heterocyclic bases that are components of these biopolymers as well as the ribose and 2'-deoxyribose sugars that are covalently linked to these bases.
Friday, April 20, 2007 (Lecture 36)
We covered a new topic today: Lipids (McMurray Chapter 27). We talked about the structures of fats and oils, how the melting temperature is related to molecular structure, and discussed fatty acids. Lipids enable compartmentalization in cells, and the phospholipids and spingolipids comprise cellular membranes. The supramolecular structure of membranes was introduced as was the structures and some functions of steroids.
Wednesday, April 18, 2007 (Lecture 35)
We finished discussing solution-phase synthesis of peptides, including the mechanism of DCC coupling. Solid-phase synthesis was briefly covered. Proteins were discussed in the context of structure and function. The forces of hydrogen bonding and hydrophobic packing were introduced as factors that influence protein secondary and tertiary structure.
Monday, April 16, 2007 (Lecture 34)
We discussed material from Chapter 26. Amino acid analysis, the Edman degradation, and carboxypeptidase degradation were covered. We started discussing solution-phase peptide synthesis.
Friday, April 13, 2007 (Lecture 33)
The average for exam 3 was 81% (revised 4/16). There was a correction implemented in the answer key on 4/16 (see the correct answers below).
Here are the approximate grade lines for Chem
39 this semester:
100-85 A to A-
84-70 B+ to B-
69-55 C+ to C
54-50 D
<50 F
We primarily discussed in class the synthesis of alpha amino acids. Reductive amination of alpha keto acids, reactions of alpha bromo carboxylic acids, the Strecker synthesis, and the amidomalonate synthesis were discussed. Basic structures of peptides were introduced.
Wednesday, April 11, 2007 (Lecture 32)
We started talking today about material from Chapter 26 on Amino acids, Peptides, and Proteins. The structures of several alpha amino acids were introduced, as was the isoelectric point (pI), which corresponds to the pH that yields a neutral (zwitterionic) amino acid.
Exam 3 was this evening. Here are the correct answers:
Form A
1. j
2. a
3. h
4. g
5. f
6. d
7. a
8. c
9. j
10. f
11. h
12. b
13. c
14. f
15. b
16. b
17. b or d (revised 4/16)
18. a
19. d
20. a
21. g
22. f
23. b
24. a
25. j
Form B
1. b
2. b or d (revised 4/16)
3. g
4. f
5. b
6. a
7. j
8. c
9. j
10. a
11. h
12. g
13. f
14. d
15. a
16. a
17. a
18. c
19. j
20. f
21. h
22. b
23. d
24. f
25. b
Monday, April 9, 2007 (Lecture 31)
We discussed reactions of monosaccarides such as glycosylation, reduction with NaBH4 to alditols, oxidation of the aldehyde to a carboxylic acid with Br2 in H2O or Ag+ / NH3, oxidation of both the aldehyde and terminal CH2OH to carboxylic acids with dilute nitric acid, the Kilinai-Fischer synthesis, and the Wohl degradation.
Friday, April 6, 2007 (Lecture 30)
Johannes led a review in class today.
Wednesday, April 4, 2007 (Lecture 29)
We continued talking about carbohydrates (Chapter 25). We began talking about reactions of carbohydrates with a discussion of Haworth projections, the difference between the alpha and beta anomers of glucose, mutarotation and the mechanism of this process.We covered alkylation and acylation of monosaccarides.
Monday, April 2, 2007 (Lecture 28)
We started talking about carbohydrates (Chapter 25) today. We discussed the stereochemical nomenclature of sugars, which includes discriptors such as (+/-), R / S, and D / L. Fisher projections of carbohydrates were discussed, as was the historical basis for the designation "D" sugars and "L" sugars. We discussed carbohydrate enantiomers and distereomers and the configurations of D-aldoses.
Friday, March 30, 2007 (Lecture 27)
We discussed the Hofmann elimination, electrophilic aromatic substitution of aromatic amines, and reactions of diazonium salts, which are prepared by treating an aromatic amine with nitrous acid (HNO2) and sulfuric acid. The synthesis of diazonium salts from aromatic amines (the Sandmeyer Reaction) is very useful because these salts can be converted into halogens, nitriles, phenols, or arenes lacking the amino group.
Wednesday, March 28, 2007 (Lecture 26)
We finished our discussion of amines. We talked about the Hofmann and Curtus amide rearrangements. These reactions allow one to synthesize amines from carboxylic acid derivatives. The mechanisms of both reactions are similar and they proceed through formation of an electron deficient nitrene, which undergoes a 1,2 shift to afford an electrophilic isocyanate. The Hofmann rearr. is run under basic aqueous conditions, and the isocyanate formed is immediately hydrolyzed to a carbamic acid that loses CO2 to form the product amine. The Curtius rearrangement does not involve aqueous conditions, and the isocyanate formed can be isolated and converted into amines, carbamates, and ureas.
Monday, March 26, 2007 (Lecture 25)
We talked about the synthesis of amines: alkylation of amines, synthesis of amines from azides, the Gabriel amine synthesis from phthalimide, nitrile reduction, and he started to discuss reductive amination.We coverved reductive amination, which is a general synthesis of amines from aldehydes and ketones.
Friday, March 23, 2007 (Lecture 24)
We finished talking about polymers. We discussed fibers, elastomers, and thermosetting resins. We started Chapter 24 on amines. We talked about how the chemistry of amines is dominated by the lone pair on nitrogen, which confers the basicity and nucleophilicy of amines. We introduced the concept of pKb, how it is calculated, and how the pKb relates to the pKa of the conjugate acid.
Wednesday, March 21, 2007 (Lecture 23)
Exam 2 was this evening. The average for exam 2 was 70%. Here are the correct answers for Exam 2:
Form A
1. e
2. d
3. c
4. e
5. I
6. g
7. c
8. a
9. d
10. f
11. b
12. a
13. h
14. I
15. f
16. e
17. b
18. c
19. b
20. b
21. e
22. d
23. b
24. f
25. h
Form B
1. b
2. b
3. b
4. c
5. a
6. h
7. I
8. f
9. e
10. b
11. c
12. e
13. d
14. b
15. f
16. h
17. e
18. d
19. I
20. g
21. c
22. a
23. d
24. f
25. e
We continued our discussion of polymers in class. We talked about radical-induced branching, copolymers, step growth polymers such as Nylon 66, and we started to discuss polymer morphology (macroscopic physical properties).
Monday, March 19, 2007 (Lecture 22)
Today, we began discussing polymers (Chapter 31). We introduced chain growth polymers today in which the polymer chain becomes longer by the continual addition of monomer units to a reactive end of the chain. We covered the mechanism of anionic polymerization of methylmethacrylate to plexiglass. The Zeigler-Natta catalyst was introduced as a method to prepare stereoregular (isotactic or syndiotactic) polymers.
Friday, March 9, 2007 (Lecture 21)
Johannes lead a review session in class today.
Wednesday, March 7, 2007 (Lecture 20)
Today, we finished discussing chapter 23. We discussed the Michael reaction, the Stork enamine reaction, and the Robinson annulation. The Michael reaction is a conjugate addition of an enolate on an enone. This reaction is catalytic in base, and is similar in that respect to an Aldol reaction. The Stork enamine reaction is another conjugate addition reaction that uses an enamine as the nucleophile (similar to an enolate). The Robinson annulation is a combination of three reactions: The Michael reaction, the Aldol condensation, and dehydration. Our next exam is on Wenesday 3/21/07. It will be comprehensive but emphasize material covered since the last exam (Chapters 20-23).
Monday, March 5, 2007 (Lecture 19)
Today, we continued discussing Chapter 23 on carbonyl condensation reactions. The Claisen condensation was introduced. This reaction requires a stoichiometric amount of base and yields beta-keto products. Mixed Claisen reactions between two different carbonyl compounds give mixtures of symmetrical and unsymmetrical products. However, the mixed Claisen can work well if one of the carbonyl compounds has no alpha hydrogens (non-enolizable).
Friday, March 2, 2007 (Lecture 18)
We started discussing Chapter 23 on carbonyl condensation reactions. The Aldol condensation of aldehydes and ketones was introduced. This reaction requires only a catalytic amount of base and yields beta-hydroxy aldehyde products. These products are readily dehydrated under acidic or basic conditions to yield enone products. Mixed Aldol reactions between two different aldehydes or ketones tend to give mixtures of products. However, these mixed reactions can work well if one of the carbonyl compounds has no alpha hydrogens or one of the carbonyls is much more acidic than the other (Knovenagel condensation).
Wednesday, February 28, 2007 (Lecture 17)
We finished discussing Chapter 22 on carbonyl alpha substitution reactions. We talked about dehydrohalogenation (elimination of HX) of alpha halo ketones, enolate alkylation, the malonic ester synthesis, and decarboxylation of beta-keto acids.We talked about the acetoacetic ester synthesis, and direct alkylation of ketones, esters, and nitriles.
Monday, February 26, 2007 (Lecture 16)
We continued discussing Chapter 22 on carbonyl alpha substitution reactions. Remember that strong bases are usually needed to generate enolates. These bases include NaH, NaNH2, and LDA. One can calculate the exent of deprotonation from the pKa values of the carbonyl compound and the conjugate acid of the base used. Bases always deprotonate the strongest acids preferentially. We covered the haloform reaction of methyl ketones. These compounds are converted into carboxylates by treatment with an excess of NaOH and elemental halogens. We talked about dehydrohalogenation (elimination of HX) of alpha halo ketones, enolate alkylation, the malonic ester synthesis, and decarboxylation of beta-keto acids.
Friday, February 23, 2007 (Lecture 15)
We started discussing Chapter 22 on carbonyl alpha substitution reactions. These reactions proceed through enol or enolate intermediates. Enols form readily in acid or base catalyzed reactions, but are typically present in very small amounts (the keto form is more stable)Enols and enolates are nucleophiles that react with electrophiles to generate alpha substitution products. Elemental halogens such as Br2 are electrophilic enough to react with enols in the absence of base. Most other electrophiles require the additon of a strong base to generate the more nucleophilic enolate. Acids, esters, and amides do not enolize sufficiently for direct halogenation to take place. However, carboxylic acids can undergo the Hell-Volhard Zelinskii reaction, which proceeds through an acid halide enol intermediate, to generate alpha halo products.
Wednesday, February 21, 2007 (Lecture 14)
We finished discussing Chapter 21 on carboxylic acid derivatives. Grignard reagents react with nitriles to produce ketone products. We started discussing Chapter 22 on carbonyl alpha substitution reactions. These reactions proceed through enol or enolate intermediates. Enols form readily in acid or base catalyzed reactions, but are typically present in very small amounts (the keto form is more stable).
Monday, February 19, 2007 (Lecture 13)
We talked about reactivity patterns of acid anhydrides, esters, amides, and nitriles. DIBAH can be used to synthesize aldehydes from esters or nitriles. More powerful reducing agents such as LiAlH4 reduce esters to primary alcohols and nitriles to primary amines. We covered the mechanisms of acid and base-induced ester hydrolysis, and the mechanism of the DIBAH aldehyde synthesis.
Friday, February 16, 2007 (Lecture 12)
We discussed how the nature of the substituents on the carbonyl group affects the stability of the derivative, the electron deficiency of the carbonyl carbon, and its leaving group properties. Acid chlorides are more reactive than anhydrides, which are more reactive than esters, which are more reactive than carboxylic acids in nucleophilic acyl substitution reactions. Steric and electronic effects contribute to control the reactivity of carboxylic acid derivatives. The Fisher synthesis of esters was discussed, as was reactions of acid chlorides, esters, and anhydrides with strong nucleophiles. Keep in mind that strong nucleophiles such as MeMgBr react with these acid derivatives to afford tertiary alcohols. The intermediate ketones cannot be isolated because they are too reactive. The Weinreb ketone synthesis is an approach that allows synthesis of ketones from the addition of strong nucleophiles to acid derivatives.
Wednesday, February 14, 2007
Class cancelled due to bad weather.
Monday, February 12, 2007 (Lecture 11)
The average for exam 1 was 75.3%.
We finished our discussion of chapter 20 today by talking about the preparation
of carboxylic acids from oxidation of alkylbenzenes, alkenes, alcohols, and
aldehydes. Carboxylic acids can also be prepared from the hydrolysis of nitriles
and the carboxylation of Grignard reagents. These compounds can be reduced
to alcohols with LiAlH4 and BH3.
Exam 1 was today. The exam scores will be posted in the lobby of Whitmore (1st floor) as soon as they become available. The scores will be emailed by the UTS to all students. If there are any score discrepancies, please see Mike in 210 Whitmore. Here are the correct answers for Exam 1:
FORM A
1. b
2. c
3. f
4. d
5. g
6. a
7. b
8. c
9. b
10. b
11. f
12. i
13. j
14. d
15. c
16. j
17. a
18. b
19. b
20. d
21. c
22. a
23. c
24. e
25. g
FORM B
1. b
2. d
3. c
4. j
5. a
6. b
7. b
8. c
9. f
10. d
11. g
12. a
13. b
14. c
15. b
16. f
17. i (corrected 2/13)
18. j
19. a
20. c
21. d
22. c
23. e
24. g
25. b
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