(b) the hydroxyl group of ethanol Correct Answer: c. (a) the hydroxyl group of 2-phenylacetic acid (b) the oxygen of ethanol Question 6 0 out of 1 points An important characteristic in the mechanism of this reaction is the formation of a tetrahedral intermediate which is the result of Selected Answer: c. protonation of the carbonyl oxygen of the 2-phenylacetic acid. Correct Answer: a. the alcohol attacking the 2-phenylacetic acid with the subsequent loss of a proton. Question 7 0 out of 1 points The Fischer esteri±cation is really an example of Selected Answer: c. an elimination reaction (either E1 or E2) Correct Answer: a. a nucleophilic acyl substitution reaction Question 8 1 out of 1 points The equilibrium of Fischer esteri±cation reactions in general is slightly towards product formation. The equilibrium can be made more favorable for product formation by all of the following except: Selected Answer: d. Increasing the concentration of H 2 SO 4 Correct Answer: d. Increasing the concentration of H 2 SO 4 Question 9 1 out of 1 points Esters can be hydrolyzed when heated with water and strong acids or bases- the reverse of Fischer esteri±cation. However, whereas Fischer esteri±cation is reversible, ester hydrolysis when carried out in aqueous base is not. This is
Due Friday, February 1:
1. Please collect your Chemistry 202 final exam from your instructor and re-write the whole thing on fresh paper, paying particular attention to anything you did wrong.
2. Please review section 7.12 (the Diels-Alder reaction) and do the following problems: Ch 7 # 32, 33, 36, 39. Also review chapter 12 (spectroscopy).
Due Friday, February 8:
1. Read Chapter 13 and answer the following questions as you go along: #3, 12, 14, 17, 18, 25, 34, 42.
2. Now try these problems at the end of the chapter: #45, 46, 54, 56, 61, 71, 72.
Finally, answer the following questions:
3. How many nonequivalent protons does anthracene have?
4. Make yourself a nice organized table describing the four major kinds of information can be obtained from a 1H NMR spectrum, and what they tell you about the structure of the molecule.
5. 3-bromo-1-phenyl-prop-1-ene shows a complex NMR spectrum in which the C2 vinylic proton is coupled with both the C1 vinylic proton (J=16 Hz) and the C3 methylene protons (J=8Hz). Draw a tree diagram for the C2 proton signal, and account for the fact that a five-line multiplet is observed.
6. Consider the set of IR, MS, 13C NMR, and 1H NMR spectra on the following page. To what molecule do they belong? Please explain your answer, especially for the 1H NMR.
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Homework #3 Due February 15th
First please try the following questions as you read through chapter 14 in your text: # 3, 9, 12, 17, 24.
Next, please try the following questions at the end of chapter 14: #31, 33, 36, 40, 42.
Finally, try the following problems:
1. Predict the 1H NMR spectra of o-xylene, m-xylene, and p-xylene, in particular the splitting patterns that would be observed for each ring proton. Label the molecule clearly to show which peaks correspond to what hydrogens. Next, predict the spectrum of 2-bromophenol, and compare to that of o-xylene.
2. Only one of nitrogens on the aromatic amino acid histidine (below) can be further protonated. Which one and why?
3. Guanine bases in DNA are nucleophilic. Which site(s) on the base would you expect to act as a nucleophile?
4. The dipole moment of THF is 1.7 D, but that of furan is only 0.7 D. Explain.
5. With what you known now about resonance stabilization of aromatic compounds, reconsider the Diels-Alder lab we did last week. Why did the dienophile add to the center ring of anthracene, and not the end ring? The resonance energies are as follows: benzene 32.9 kcal/mol; napthalene 61 kcal/mol; anthracene: 84 kcal/mol.
6. What is the product of a Fridel-Crafts reaction of benzene with 2-chloro-3-methylbutane (in the presence of AlCl3)?
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Homework #4 Due Friday February 22nd
After Monday's lecture, please read up through-and-including section 15.7, and try the following problems:
Chapter 14 #47. Chapter 15: #5 (show resonance structures), 9, 14, 16, 34, 41, 57.
After Wednesday's lecture, read the rest of the chapter and do the following problems:
Chapter 15: #36, 46, 49, 54, 56.
Finally, try the following problems:
1. There are five resonance structures for phenanthrene. Draw them all.
2. A particular type of electrostatic interaction called a “cation-pi” effect was first predicted then experimentally observed in proteins between cations and the aromatic protein side chains tryptophan, tyrosine, and/or phenylalanine. Thinking about the electronic distribution in aromatic systems, explain why a cation might want to bind electrostatically to the face of an aromatic ring.
3. Explain using resonance structures why the pKa of phenol is around 8.9, while the pKa of tyrosine is closer to 10.1.
4. Why do Friedel-Crafts alkylations give polysubstitution products, but F-C acylations do not? In what ways can alkylation of benzenes be achieved while avoiding this problem?
5. Propose syntheses for the following molecules starting from benzene. In doing so, draw the target molecule, identify the substituents, and recall how each group can be introduced separately. Then, plan it out either forwards or backwards (retrosynthetically), pointing out along the way the reactions that you didn't choose because they won't work. Don't be afraid to show your work or your thinking processes.
b. 4-chloro-2-propylbenzenesulfonic acid
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Due Friday February 29th
To review for the exam, please do the following problems from previous chapters:
Chapter 13 # 5 (please also predict the integration and splitting for all three isomers), 13, 20, 30, 37, 50.
Chapter 14: 26f, 27, 28, 29, 49.
Chapter 15: 15, 17, 24, 31, 37.
Then try these problems from the new chapter:
Chapter 16: 2abcde, 4, 6, 9, 15, 20.
Finally, consider the following:
1. Imagine that a protein active site containing either tyrosine or phenylalanine is to be modified with an electrophile. Which should be more readily reactive with the electrophile, and at what position(s) on the aromatic ring would you expect electrophilic substitutions to occur?
2. Of the different kinds of type I carbonyl compounds shown on page 737 esters, amides, and carboxylic acids are common functional groups in biological molecules, occurring in (among other things) proteins, fats, and nucleic acids. Acid chlorides and acid anhydrides, however, are not found in biological systems. Why not?
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Formal due date: Monday March 24, 2008
NOTE: I will answer any and all questions about this homework in class on Friday March 14th and collect it then from anyone who wants to turn it in before Spring Break.
Please try the following questions from Chapter 16 after the lecture on Wednesday 3/5/08: # 40, 41, 53, 56, 60, 64, 75, 81.
Then please try the following questions from Chapter 17: 45, 48, 49, 53, 60, 61, 65, 66, 71, 75.
Finally, consider the following additional questions:
1. Oxidation-Reduction Reactions. On a separate piece of paper, list all of the oxidation-reduction reagents we have seen so far, including a description of their reactivity, in two charts ("oxidants" and "reductants"). You may wish to list what each does not react with as well as what it does react with (i.e. H2(g) with Pd/C generally does not reduce benzene, except under high pressure). Rank them according to which seem to be stronger than others. We will add to this list over the next couple of chapters.
2. Ester Hydrolysis. In lab later this semester you will prepare soap from various common food oils by heating the oil in a strong base, a process called saponification. Write an equation and mechanism for this transformation of oil (triacylglycerol) to soap (fatty acid salt) by base, and another equation and mechanism for the acid-catalyzed process.
3. Amides. The enzymatic formation of amide bonds in new proteins by the ribosome is the opposite reaction of the amide hydrolysis catalyzed by proteases such as chymotrypsin. Which reaction is energetically favored, amide bond formation or hydrolysis? How is the unfavorable reaction made to happen in the cell? How is the favorable reaction prevented from happening all the time in the cell?
4. Acetals and Ketals. As shown in class, D-glucose can spontaneously form a 6-membered "pyranose" ring by intramolecular formation of a hemiacetal. D-fructose can form a 5-membered "furanose" ring in an analogous way.
(a) Show how this occurs. Draw the product in both a Fischer and Haworth projection. (b)Why does a stable tetrahedral product form in this reaction, instead of expelling a leaving group and reverting to a carbonyl-containing product like a carboxylic acid or ester?
(c) What is this kind of molecule called? (not a hemiacetal but....)
(d) How many isomers are generated by this reaction? Why? Would you expect them to exist in equal amounts? Why/why not?
5. Extra credit. See paper handout for reactions.
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Homework #7: Carbonyls
Due Wednesday April 2, 2008 IN CLASS
Please do the following problems from Chapter 18: 8, 12, 25, 29, 49, 54, 55, 56, 57, 59, 62, 63, 69.
1. Explain how the reactions in this chapter are similar to one another, and how each is different.
2. Propose a mechanism for the condensation-then-dehydration reaction of cyclopentadiene with acetone to form a fulvene. (Hint: One of the reagents, "X," is generated from cyclopentadiene with base. What do we remember about cyclopentadiene from the aromaticity chapter? What will the base do to it?). See paper handout for reactions.
Due Wednesday April 16th
First please answer the following questions in Chapter 22: Amino Acids and Proteins:
# 1, 2, 5, 31, 32, 52, 53, 64,
Then please answer the following questions:
1. Sketch the resonance structures for the peptide bond. Which atoms are in the same plane?
2. Why do replacements of lysine with arginine, and leucine with isoleucine, usually have little effect on protein structure or function?
3. Which nine protein groups are ionizable at biologically-achievable pH’s? Draw their neutral and ionized structures and indicate what fraction of each form would be present at pH 6.8. (use the pKa values on pg. 1025. Use just one average value for the N and C termini-don’t calculate them 20 times over!)
4. Draw two pairs of possible electrostatic interactions between amino acids.
5. Why do electrophiles added to proteins often react with tyrosine?
6. What protein side chains might be used to stabilize the binding of a Mg2+ ion or similar cation?
7. What protein side chains might be used to stabilize the binding of ATP in a protein binding site? (hint: the adenine base in ATP is aromatic, and the three phosphates have a cumulative charge of -4.)
8. Use simple thermodynamic arguments to explain why proteins denature at elevated temperatures. Some organisms called hyperthermophiles live at extremely high temperatures, such as hot springs and the volcanic vents at the bottom of the oceans. How must their proteins be different from ours in order for this to be possible?
9. What are enzymes?
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Due Friday April 25th
Chapter 19 (Oxidations and Reductions): #31, 32, 33, 35, 38, 42, 45.