Exam 1 Solutions | Organic Chemistry II | CHEM 30B, Exams of Organic Chemistry

Download Exam 1 Solutions | Organic Chemistry II | CHEM 30B and more Exams Organic Chemistry in PDF only on Docsity! Chemistry 30B Winter 2004 Exam 1 Solutions Page 1 A note about exam keys: The answers presented here are usually significantly longer than expected from a student taking the exam. An exam key serves not only to reveal what was expected, but to instruct you as well. Exam key posted 9 AM, Friday, February 6, 2004 Statistics: Average score and standard deviation are meaningless, as your course grade is determined only by the fixed grade scale established before the course started. To see the grade curve, consult the Chem 30B Home Page. 1. (a) OH OH excess CrO3 aq. H2SO4 CO2H O (b) CH3CO3H O (c) OH NaH O Na 2. Alkoxide: Any anion of the general formula RO-. Example: CH3O - (methoxide). Williamson ether synthesis: Reaction of an alkoxide (RO-) with R-LG (LG = leaving group), by an SN2 mechanism, to form an ether. Oxonium ion: Any molecule having an oxygen atom with three bonds and a positive charge. Example: CH3OH2 +. PCC: Pyridinium chlorochromate. Used to oxidize primary alcohols to aldehydes, or secondary alcohols to ketones. NH CrClO3 PCC RCH2OH PCC R H O R C R' OH H PCC R R' O Chemistry 30B Winter 2004 Exam 1 Solutions Page 2 3. Hg(OAc)2 HgOAc + OAc HgOAc HgOAc CH3 H2O O HgOAc HAcO H OH HgOAc 4. CH3OH CH3 (TsCl)S O O Cl N (pyridine) CH3OTs 5. CH3S O O CH3OTs = CH3O 6. OTs is a very good leaving group because it gains resonance stabilization of its negative charge upon departure. R OTs CH3 S OO O CH3 S OO O CH3 S OO O 7. CH3OTs KF DMF CH3F 8. Reaction A has an epoxide. 9. Reaction A is faster. 10. Ph O H OH2 Ph OH OH2 Ph OH H OH2 O H Ph OH OH 11. Reaaction A is faster than reaction B because reaction A is assisted loss of the epoxide ring strain, whereas reaction B does not have this assistance. 12. PCl3 looks like PBr3, which convert alcohols to bromides by an SN2 reaction of Br - on an ROPBr2 intermediate. Therefore we predict: