Exam III Answer Key - Organic Chemistry I | CHEM 3311, Exams of Organic Chemistry

Download Exam III Answer Key - Organic Chemistry I | CHEM 3311 and more Exams Organic Chemistry in PDF only on Docsity! 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 Recitation TA's Name Recitation Day & Time Grading Information Page # 2 NOOR W General Instructions received unauthorized assistance on this work." 15 20 15 20 20 10 Points Possible Your Score TOTAL (out of 100) (1) This is a 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-3-Hexene (C) trans-3-Hexene (D) 2-Methyl-2-pentene (ii) When 2-methyl-2-butanol is treated with H2SOx at 80°C, 2-methyl-2- butene is the major product. What is the mechanism for this reaction? (A) Snt (B) E1 (C) Sn2 (D) E2 (iii) When cyclohexy! 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) Snt (B) E1 (C) Sn2 (D) E2 (iv) What is the organic product obtained when 1-butene is reacted with HBr in the presence of peroxides? (A) 1-Bromobutane (B) 2-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 bond? (A) Hydroboration-oxidation (B) Brz in water (C) He in the presence of Pt (D) Epoxidation CHEM 3311-200, Exam 3, Page 5A Name: 3. (20 points) Complete the reaction by filling in the reactant(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. ° Oo — Ul A. Hox p< BA _HjC-C-ONa HO 'H,-O-C-CH, + NaBr \_ fe CH;COOH ° } B. CH,(CH,))sCH,CH,CL KOCH) on, (2), CH= CHy DMSO, 25°C ~ a Na ¥ of RS uw Bry tiny + a Cc. (E)-2-Pentene cee ess Be CCl, Btz Pa (z)- ZRutene ——4 > (2, 3R)~ and 4H Cet, (28, 3&Y- 2,3- dobro pawtowne- aN D. 2-Methyl-2-butene __ Bp = Be Ss Be H,O R AS de i 2 at is oy + WK, Ina ar = H 4 & . E. 1,5,5-Trimethylcyclopentene ea 4 a < ewawlirneve 2. H202, HO hy, Hoh H heat (major) (minor) H «. >= 1 Ha(OAc)y, HO -— LNB, NaBHy OH CHEM 3311-200, Exam 3, Page 6A Name: 4. (10 points) Circle the mechanistic symbols (Swi, Sn2, E1, E2) that are most consistent with each statement. (A) Reaction of methyl bromide with sodium ethoxide in ethanol proceeds by this mechanism. Sni Sn2 El E2 (B) These reaction mechanisms represent concerted processes. Sut Sn2 El E2 (C) These reaction mechanisms involve carbocation intermediates. Sui Sn2 El 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-Butyl azide from (R)-sec-butyl alcohol D) OH v6 5s sonvert bo Ny H 2 OTs j HOH ag a (S)- aa (Rp see- Butyl te oi (R)-see- Buty Lokeakk. 00. ib Gyr ahs ewrenil, Na N3 Tsck note: Actenutow. tu: DMSO ye e ee wf “vast 6B) UCHs)sC-O-CHs from an alkyl bromide Eee ap cH, fo - CCH) => CH; Br KOCH OR 3 me DMSO (rsyofomens =p Grohe Se 3) Hg(eAc),? KTOdeH3) of cH aoe, 2) NaBH, CHEM 3311-200, Exam 3, Page 7A Name: 6. (10 points) Draw a stepwise mechanism for the reaction shown, You must show the arrows, lone pairs, and formal charges to receive credit. Pe f Step 1: cof ™ oS SR. ==? ots . sagexpansen | Step 2: ce Hing pers Cy = CL 2 * noxheodlorn 2 carbocation H el ANE oN Step 3: CET, Noo? Or oly Le i H Hw H Sy ey / + Nee Gop Gut Co + ey ONLY ®