exam3_key - ANSWER KEY CHEM 3311-200 Exam 3 By printing my...

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Unformatted text preview: ANSWER KEY CHEM 3311-200 Exam 3 November 15, 2007 By printing my name below, I pledge that "On my honor, as a University of Colorado at Boulder student, I have neither given nor received unauthorized assistance on this work." Name Recitation TA's Name Recitation Day (St Time Grading Information Page # Points Possible Your Score 2 15 20 15 20 20 10 Nam-taco TOTAL (out of 100) General Instructions (1) This is o CLOSED BOOK exam! No notes and molecular models are allowed. (2) You have 2 hours to complete the exam. You may not leave the room during the first 90 minutes of the exam. (3) Write your name at the top of each page, starting with page 2. (4) Use the back of exam pages for scratch paper. (5) If caught cheating, you will receive at best an F for this exam. The instructor reserves the right to proceed further in compliance with university policies. CHEM 3311—200, Exam 3, Page 2A Name: 1. Multiple Choice Questions (15 points) (i) Identify the most stable alkene. (A) 1—Hexene (B) cis-B—Hexene (C) trans-3—Hexene (D) Z—Methyl-Z-pentene (ii) When 2-methyl—2—butanol is treated with H2504 at 80°C, 2-methyI—2- butene is the major product. What is the mechanism for this reaction? (A) 5N1 (B) E1 ((3 5N2 (D) E2 (iii) When cyclohexyl chloride was treated with sodium ethoxide in ethanol at 55°C, cyclohexene was obtained in 100% yield. What is the mechanism for this reaction? (A) 5N1 (B) E1 (C) 5N2 (D) E2 (iv) What is the organic product obtained when 1-butene is reacted with HBr in the presence of peroxides? (A) l-Bromobutane (B) Z-Bromobutane (C) 3-Bromo-1-butene (D) 1,2—Dibromobutane (v) Consider the addition reactions of alkenes. For (E)—2—butene, which reaction conditions will NOT lead to net syn addition to the double band? (A) Hydroboration—oxidation (B) Bra in water (C) H2 in the presence of Pt (D) Epoxidation CHEM 3311-200, Exam 3, Page 3A Name: 1. Multiple Choice Questions (20 points) (vi) Which alkene will react at the fastest rate in 50%. H2504? (A) Z-Methyl-Z—butene (B) 1-Butene (C) cis-Z-Butene (D) trans-2~Butene (vii) A dimethylcyclopentene was identified by ozonolysis; zinc was included during the hydrolysis step as a precautionary measure. The only product obtained was OHC—CH(CH3)-CH2—CH(CH3)-CI—IO. Identify the compound. (A) 1,2-Dimethylcyclopentene (B) 1,3-Dimethylcyclopentene (C) 3,5-Di-methylcyclopentene (D) 4,4-Dimethylcyclopentene (viii) Which constitutional isomer reacts fastest with NaI in acetone? (A) 2—Chloro—2—methylpropane (B) 2-Chlorobutane (C) 1—Chloro-2—methylpropane (D) 1-Chlorobutane (ix) What is the major product in the reaction between 2—methylpropene and Bra in H20? (A) 3—Bromo-2-methylpropene (B) 1,Z-Dibromo-2-methylpropane (C) 2-Bromo'—2—methyl-1-propanol (D) 1-Brorno-2-methy|~2-propanol (x) Compound X is optically active. Hydrogenation of this compound produced methylcyclopentane. What is the identity of compound X? (A) Methylenecyclopentane (B) I—Methylcyclopentene (C) 3-Methylcyclopentene (D) 4—Methylcyclopentene CHEM 3311-200, Exam 3, Page 4A Name: 2. (15 points) Show the arrow—pushing mechanism (including lone pairs and formal charges) for the reaction of (Z)-2-Pentene with peroxyacetic acid in CH2CI2. (A) If two stereoisomers are formed, for each product, label all chirolity centers R and 5 as appropriate. (B) Write a complete IUPAC name for each product. (C) Clearly state the relationship between the stereoisomeric products as diastereomers, enantiomers, or mesa form. Circle your answer! CHEM 3311-200, Exam 3, Page 5A Name: 3. (20 points) Complete the reaction by filling in the reoctont(s) or' product(s) as appropriate. If stereoisomers are formed, show each one with the correct stereochemistry and label as diastereomers, enantiomers, or' meso compound. 0 11 0 A. Ho (3 Ba, H3000“ H0 .11 43—35011 + NaBr Q *2 CH3COOH 2 3 B. CH3(CH2),5CH2CH2c1 w... (3H3 (CH2): CH_—._CHA DMSO,25°C 5 {5/1, \_./H H is: 53% s ' $H Hm Brz m + ‘1‘ C. (E)-2—Pentene ____—___,_ J? H H CC]4 "' . 35% 333 .ewwwamvub (z)- z-Rmm “—5, (22% 3e - amoL . HWH 001‘; (231,35 _. 313‘ cub/LOW WWI-- /—\_._.. Brz D. 2-Methyl—2-butene .5 R 32, .3 :33, H20 >Y ‘9 mew %/ H C 9,; + H0 ”(H 1 BH T F K - E. l,5,S—Trimethylcyclopentene -—-—'—n-3 H Sr,“ 3 fimW 2. H202 HO- 3'4, I HH . OH! HO? OH F. heat (major) (minor) H >fl 1. Hg(OAc)—H2—’,H20 s- H 2. NaBH4 5H CHEM 3311-200, Exam 3, Page 6A Name: 4. (10 points) Circle the mechanistic symbols (5N1, 5N2, E1, E2) that are most consistent with each statement. (A) Reaction of methyl bromide with Sodium ethoxide in ethanol proceeds by this mechanism. 5N1 5N2 E1 E2 (8) These reaction mechanisms represent concerted processes. 5N1 5N2 E1 E2 (C) These reaction mechanisms involve carbocation intermediates. Snl 5N2 E1 E2 5. Organic Synthesis (10 points) Outline an efficient Synthesis of each compound from the indicated starting material and any necessary organic or inorganic reagents. (A) (S)—sec-Buty| azide from (R)—sec-buty| alcohol CHafO-M C(Ci-ljg 57>- CH5 Bil, +.... W (CH3 23%};0— 0H3 __—_> (04ng fl 3%, 1 H one): i<+6 an ) ) jg” 02H\—- /‘£T‘:BL:(OH33 2) NO‘BH4 ’ ' awuso . . CD 53 W E. WBfith-O-Cm from an alkyl bromide ijpuue. ”I CHEM 3311-200, Exam 3, Page 7A Name: 6. (10 poin’rs) Draw a sfepwise mechanism for The r'eacTion shown. You must Show The arrows, lone pairs, and formal charges To receive credit 6” 6%%15 “4114/3814 -———?’ d\ 2, cmbraadlw 5W: 2,; d\ M 6" mm y; (V H I o /H IA @50.~\H :0 _.,_7, 5%; 3-5 W F H 69 RHmo/ / H H\ H O. O _ “N." - H ...
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