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Unformatted text preview: Name _______________________ F.03.210E2 Page 1 PNC Professor Finds That MTBE Additive Threatens Drinking Water in States Where it is Not Routinely Used
WESTVILLE - An ongoing survey of gas stations in the Midwest reveals that MTBE, a common gasoline additive, is present in sites where it is not routinely used, posing a growing threat to ground water in these areas, according to Reynaldo Barreto, Ph.D., an associate professor at Purdue University North Central in Westville, Ind., and the study’s lead investigator. The study was described by Barreto on Aug. 30 ,2001, at the 222nd national meeting of the American Chemical Society, the world’s largest scientific society, held in Chicago. http://www.pnc.edu/cd/news/mtbe.html I. (20 points)
MTBE is methyl t-butyl ether, (CH3)3COCH3, a common (albeit controversial) gasoline additive. (a) Complete the following reaction, in which MTBE is prepared as a product. You should also provide the curved arrow mechanism for the reaction.
complete this balanced chemical reaction and provide the curved arrow mechanism CH3 CH3 C CH3 + O Na CH3 CH3 I tBuONa = 2 arrows = 2 CH3 C CH3 CH3 O + Na IH 4 methyl t-butyl ether MTBE (b) Provide an Energy Diagram for the formation of MTBE. Include the level of the starting materials (label as "SM"), the products (label as "P"), and any intermediates (label as "I-1," "I-2," etc), along with the energy curve(s) that relate them to E each other. The overall reaction has a DG˚ of -10 kcal/mol, and an activation energy of +25 kcal/mol.
5 kcal/mol SM/P @ -10 = 2 one curve = 2 E A @ 25 = 2 SM P progress of reaction (d) How many signals will there be in the H-NMR spectrum of MTBE? (e) What will be the ratio of the size (area) of the H-NMR signals? 6 (c) Provide a drawing of the anticipated transition state structure for this reaction. Dashed lines should be used to represent partially forming or breaking bonds, and any partial charges should be indicated. You do not need to show the sodium ion. 2 2 3:1 (9:3 is ok)
2 CH3 CH3 d C O CH3 d I CH3 no partial credit 4 (f) How many signals will there be in the C-NMR spectrum of MTBE? 3 2 II. (33 points)
A. Compound A is an amino acid that was prepared during the synthesis of Belactosin A, a substance that shows modest antitumor activity. (a) Circle each stereocenter in Compound A and provide the configurational label.
Compound A Name _______________________ Page 2 F.03.210E2 R H S H2N O HH NH2 H H O H no no HH S 7 "R" center = 3 "S" centers = 2 ea 2 2 (b) Is Compound A optically active? (c) Is Compound A dextrorotatory? (d) Is there a compound that is enantiomeric to Compound A? Circle one: Circle one: yes yes cannot predict cannot predict no no Circle one: Circle one: yes yes cannot predict cannot predict 2 2 (e) Is there at least one compound that is diastereomeric to Compound A? B. For each of the following pairs, check all of the classifications that apply (no partial credit). (a) (b) Cl H O X enantiomers the same molecule diastereomers constitutional isomers H X stereoisomers Cl X different molecules X both are optically active conformational isomers 3 O X enantiomers the same molecule diastereomers constitutional isomers X stereoisomers X different molecules X both are optically active conformational isomers 3 CH3 CH2CH2OH C OH CH3 OH HOCH2 (d) C CH3 CH2CH3 enantiomers the same molecule diastereomers X constitutional isomers stereoisomers X different molecules both are optically active conformational isomers 3 (c) enantiomers X the same molecule diastereomers CH3 H constitutional isomers CH3 H Cl Cl stereoisomers CH3 CH3 different molecules Ph Cl H Cl X both are optically active conformational isomers 3 H H H H H Ph NOTE: If 2 molecules have different properties, then they are different molecules! (R)- and (S)-stereoisomers have opposites signs for optical rotation. C. Provide the complete IUPAC name for the following molecule. H H Cl (R)-1-bromo-4-chloropentane -2 for each class of error: stereolabel, punctuation, numbering, H CH2CH2Br 6 prefix labels, ordering labels, root name CH3 H Ph H Ph H H III. (20 points)
A. This energy diagram represents a chemical reaction where the starting material (Compound S) exists as a mixture of forms (S1 and S2) that are in equilibrium. The S1 form gives one product (Compound W) while the S2 form give another product (Compound Z). Name _______________________ Page 3 F.03.210E2 E S1
progress of reaction S2
Z Reversible reactions are indicated with double arrows: Irreversible reactions are indicated to be in the direction shown by a single arrow: (a) under the following conditions: W (b) under the following conditions: W S1 S1 S2 S2 Z Z Which product predominates? Which product predominates? W Z 3 3 B. The electrophilic addition of HCl to 1,3-butadiene gives a mixture of three products: H H C H C C H H C H HCl H H C H C C H C H H H H H Cl C C C H HC H H
Product Q H H Cl C H H Cl
Product P HH CH CC H 1,3-butadiene Product R (a) Provide the complete, step-wise, curved arrow mechanism for the formation of Product Q, Cl H H C H C C H H C H H Cl H C H H C C H carbocation = 2 H C H H H H C H C C H mechanism = 2 H C H H H H H Cl C C C H HC H H 8
Product Q mechanism = 2 resonance form = 2 (b) What is the stereoisomeric relationship between Products Q and R? DIASTEREOMERS 3 (c) What is the stereochemical configuration of Product Q? E 3 IV. (28 points) Name _______________________ Page 4 F.03.210E2 OH H H CH menthol CH3 A. Menthol is a naturally occurring compound found in the oils of the mint tree Mentha arvensis. Menthol is well known for its cooling effects and its mint flavor and odor, which are the basis of the majority of its uses. The single H largest use for menthol is probably in cigarettes. A survey of pharmaceutical products indicates that menthol is CH3 formulated in over-the-counter rubs and liniments (2-10% concentrations), antipruritic lotions, nasal sprays, expectorants, mouthwashes and sprays, cough drops, and foot powders. http://ntp-server.niehs.nih.gov/htdocs/LT-studies/TR098.html CH3 (a) Provide the complete IUPAC name for menthol; you do not need the stereochemical labels. 2-isopropyl-5-methyl-1-cyclohexanol -2 for each class of error: punctuation, numbering, prefix labels, ordering labels, root name, suffix 6 (b) Draw the two chair conformations of menthol. Place the more stable form on the right (the groups shown on menthol, above, are the ones that should be included). less stable chair form here CH3 H H CH acceptable chair form = 2 H3C each directionality or stereo error = -2 more/less stable reversed = -2, once B, Org. Lett. 2003, 5, 3947. (a) Answer the questions about Compounds J and K with respect to Compound H. HO CH3 H N OH H CH3 H3C H HO N
Compound J more stable chair form here OH H3C H H H3C CH3 8 CH H H OH CH3 acceptable chair form = 2 each directionality or stereo error = -2 more/less stable reversed = -2, once is the enantiomer of H has an S center and an S center the same molecule as H X is a diastereomer of H X is optically inactive X is a meso isomer X has an R center and a S center is optically active has an R center and a R center X is the enantiomer of H has an S center and an S center the same molecule as H is a diastereomer of H is optically inactive is a meso isomer has an R center and a S center X is optically active X has an R center and a R center 8 H OH CH3 3 (b) Compound H Check off all that apply; no partial credit. HO H CH3 N H OH CH3
Compound K 3 V. (19 points)
A. Draw the Newman projection for the C2-C3 bond of this conformation of this molecule, using C2 as the front atom. H OH O
5 Name _______________________ Page 5 F.03.210E2 staggered = 1 conf = 2 stereo = 2 ea H Br if connectivity is WRONG, then -3 points at the end (but not H3CO to go <0) O OCH3 OH CH3 H3CO 4 3 2 1 OCH3 CH3 Br 7 B. Provide the curved arrow mechanism as well as the intermediate that results when the following carbocation (carbocation W) combines with ethanol (CH3CH2OH). Then, using another ethanol molecule as the only other available chemical reagent, provide the mechanism that converts the intermediate you have drawn into the product (product X). Provide the other product in the balanced equation.
mechanism here intermediate plus mechanism of reaction with ethanol here OCH2CH3 C CH3 product X + CH3 C CH3 CH3 CH3CH2OH mech = 2 intermed = 2 + CH3CH2OH H OCH2CH3 C CH3 2 CH3 4 other product here carbocation W CH3CH2OH2 no partial 2 C. NMR spectroscopy provides powerful information for helping to determine molecular structure. The following addition reaction is unfamiliar to you. However, based on the H-NMR and C-NMR information, as well as the chemical information provided, you can figure out what the major addition product of this reaction must be.
draw the expected major regioisomer H C H C OCH3 a mixture of Br2 and CH3OH H Br H no partial C C OCH3 OCH3 CH3 4 + a minor regioisomer + HBr is a by-product from both the major and the minor products in the balanced equation CH3 Experimental data on the major regioisomer: molecular formula: C5H11BrO2 H-NMR: 3 signals; area ratio 2:6:3 C-NMR: 4 signals ...
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This note was uploaded on 01/28/2011 for the course CHEM 210 taught by Professor Kiste during the Spring '10 term at Michigan Flint.
- Spring '10