Chemistry 21 Final Exam Solutions 2010

Final Exam Chem 21 Dec 18, 2009 Name page 1 (30) 2 (55) total (300) 3 (40) 4 (45) chk 5 (40) 6 (40) 7 (30) 8 (30) Please resist the urge to write in this space. 1. (20 points) Draw the following compounds. Show stereochemistry clearly. (a) (E,S)-2,3-dichloro-1-phenyl-1-pentene CI (b) (R)-1-(bromomethyl)-3-propylcyclobutene Br (c) Draw the product of an S2 reaction of the compound in part b with CH3CO₂Na. 2. (10 points) The amide below can be protonated on O or N. Draw the most stable conjugate acid, including any important resonance structures. 14 NH -14 NH CH 30 3. (20 points) (a) Write the acid-base reaction of acetone (CH3COCH3, PK, 20) and NaH. Draw all structures clearly, and illustrate the reaction with curved arrows. CH₃ HE -CH pKa=20 + HO shouge acid (Shise) CH G -CH2 Do (uk CH3-CH() base عم Ha pka =35 meaked (b) Label the acids with their pKas, and label the stronger and weaker acids. (c) Does the equilibrium lie to the right or the left? right (d) Based on your pKas, what is the numerical value of the equilibrium constant? Ken = 1015 (e) Based on your answer to part d, estimate the AG° of the reaction. 15x113 20 00°=-20 kcald 4. (35 points) Draw the organic products of the following reactions, showing stereochemistry clearly. Indicate any products that are enantiomers or disastereomers. 1. OsO4 1. BH3 CH CH 2. aq Na2SO3 2. H2O2 aq OH- (achixel) enants. Bv Br2 D-Cl CI D CH₂ CI L H+ (ach.) CI (achral) CICH KOH CI drastus. (ach.) H₂O via 23 ream. page 2 55 5. (13 points) Which of the diazonium ions below would lose N₂ more rapidly? Briefly explain your choice. (A clear but brief answer will likely require structures.) NEN A NEN: B B loses N₂ much ace avament bocation av an 4e cycle anti-avomatic 6-agle- aramatic 6. (12 points) When treated with potassium tert-butoxide, the two stereoisomers E2 elimination at very different rates. Which stereoisomer reacts more rapidly trans and why? (A clear but brief answer will likely require structures.) below undergo the cis or the (CH3)3C Br Br (CH3)3C Br prefenes conf has B-Hs anti to lis B na B-Hs anti (E2 here would have to go vra higher-Edsax. Conformer) 4 H CTS does El ryn ~500x faster than kans. 7. (15 points) A fledgling chemical company has hired you as a consultant to determine the structure of an unknown hydrocarbon ("Compound-X"), having the formula C10H16. Compound- X reacts with 2 equivalents of H2 gas in the presence of a Pd catalyst to produce 1-isopropyl-4- methylcyclohexane. Ozonolysis of Compound-X gives the products shown below. The company will pay you $1,500 (and 15 points) if you can draw the structure of the mystery hydrocarbon in the box. 1. O3 (excess) 2. (CH3)2S + H₂C=O 0 "Compound-X" must have this connectivity of Cs +2 d. b.s 'this "reconnection" makes a 6-membered rong. page 3 40