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Unformatted text preview: Circle one: | wish to have my exam I wish .to pick up put in the rack. my exam. Printed Name (Please print clearl Signature CHEMISTRY 252 Final Exam May 9, 2007 200 Points 8:00-10200 AM This exam has 9 problems on pages 2 through 12. RULES 1. The use of a calculator and model kits are not permitted. 2. This exam is closed book and closed note. No aids other than writing implements are permitted. 3. Answer the questions in the spaces provided on this exam. 4. If you wish to ask a question about procedures or about a problem on the exam, raise your hand. 1__ 7.____ 2____ 8__ 3._ 9____ 4.______ 5._‘ 6. TOTAL: /100 1. Predict the major product or products that you would expect to be formed in ten of the following fifteen reactions. If you feel that no reaction will occur, then answer no reaction. Be sure to answer only ten problems. If you answer more than ten, then only your first ten will be graded. (40 points] 4 pts. each) 0.. C3 NagCr207 ‘a’ 000 ’ H2804 1) BH3 2) P00, CH2Cl2 (b) : : 3) Ph P CH 3 = 2 ! O fir Mae 0H E120 S/j 1)n-BuLi o 2) CH2=CH-CH2-Br l (d) S ___. 3) W, H20, HgCI2 1) EtNHg, Na2003 /& (e) Cl m 2) LiAlH4 \ N OH ‘ O a [for do“ excess l2 CHO 1) Bra. H20 ...(5 (9) HO H 2) F92(SO4)3. H202 U" H OH 3) NaBH4 5‘ Oi CHZOH ( 1‘42 0 L} (k) (I) 0 Br 1 equiv. 'NH2 Br 0 NH3 1) excess MeOH, HCI 2) H2, Pd on carbon 04° H 3) HCI, excess H20 M452 1) Mel - H 2) A920 - "’Me 3) heat H 1) NaOEt, EtOH 2) CH2=CH-CH2-Br OEt 3) H+, H20, heat Me0\[:l 1) HN03, H2804 2) Fe (or Sn), HCI OH : 0 N82CO3 0H 1) (00002, CH2012 N32003 2) MegCuLi 0 1) NH3, HCN H 2) w, H20 4 Fill in the reagents needed for accomplishing five of the eight following transformations. More than one step may be required. Be sure to answer only five problems. If you answer more than five problems then only your first five will be graded. (20 points/ 4 pts. each) 06%, ”to OH 9) Featsmlw ”Dob HO OH HO H OH ,0 OH H HO H o 0 ”“05 ”2,6621 ' b 62298 La $14! HCQ ) we at l+0~10=010r puma) QM til mow C) (:6 l1 M11514 4) imam O _ OMe 0 (Le J‘Cfl5 / AICQ5 OMe o d) E: a) Mm,Nlla,CL),-l—OI—l ©XCH O D l—H’ I Miami, WQ) 0 e) OH WW/W , Me J) ”Rf/Wt; Me DWI/Ilqlflqlw “Mafia 0 93pm 7WD N N Ph 0 [EACH 55 MLp’MMM Q) 01/0 Hanna! mung CON h) :OMG W3}? dN-Me " smmba- 3. a. Write a curved arrow mechanism for the following reaction. (5 points) Mm NalelgatMeOH O {7 0&1: O CE;=¥h ‘ 0% FAG W § 0 pit/5M9 191+ 0“ 0%: LIVE b. Why does the reaction selectively form the product at GB of the ketone instead of C1? (5 points) m 0%} lqu’ ”QICQ r61 ‘HUZ Paw/(1674 )5 ‘MCQ 74440112 almtnaflm. was “be possible-£1 a Webb/IE 3%”) WV, Obi CI here c. The reaction in part a does not give the aldol product (B-hydroxy carbonyl). The aldol product can be synthesized using a strong base as illustrated below. Why the selectivity for CS vs. C1 in this case? (5 points) 0 1) LDA, THF ‘ O : If -73 °C ”+1 H20 : j OH _ 2) 0 "gentle" workup Ph ‘ Rim/ilk, oQJLprOWLO‘VlaW . d. Why can the reaction in part c be used to make the aldol product when the NaOMe, MeOH conditions used in part a can not be? Please restrict your answer to no more than two sentences and an appropriate drawing if you find it helpful. (5 points) ” W 0174 CO Linglig‘iL? 2%3‘a C1540 Ln'l’iMSQJsQU u‘l. librwhcnecmllmcms lanai/57%; 4. Design a synthesis offi the following tripeptide using any t Boc protected amino acid you need and the reagents DCC, trifluoroacetic acid (TFA), NaZCOSLnd Merrifield’ s resin (also illustrated below). (10 points) W H C) +\)0L ”Ki Boc/Molt H N N - Ph/ m, Merrifield resin CD H4: 7 - I+ C9 , ,4 ll d WWW H- I 0 coat) V‘O WW' ' \x“ ”I” We 60¢ \0 Dec, 0 K 5—; 0 6“" 61%} I H 5. For each set of molecules below, please rank the indicated bonds in order from highest wave number (assigned the number 1) to lowest wave number (assigned the number 3). (12 points/ 3 pts. each) 'i ii ' a) it“; “Li/Nil uni/O"; 3_ - :2. L 90 _>0 __>O b) RJLOMe RJLH R NMe2 J_ i _3_ l / H / H c) — \ _l_ él___ 3__ \ T \ H \ D a) (j (3 L _l_ L e. Explain your answer for the aldehyde vs. amide case above in part b. In other words, support your answer with a mechanistic picture for why the relative wave numbers are what they are. (4 points) Q 0p 09 (2256mm W5 ll Jk’bl/ M 6”) ¢J§C3w Wig mew ((3:9) W A” bold. f. Explain why your answer to part e is consistent with aldehydes being less stable than amides. (4 points) 925mm Wm M» CFO 1067109 ) my: Wu WWW magmwmw Warsaw film/2W mg+€<2m€2wee. 6. The following esterification was recently performed here at Washington University. a. Below are two proton NMR spectrum showing the non-aromatic region for the starting alcohol (spectrum l) and for the product (spectrum II). In the product spectrum, please note that the triplet at 1.6 ppm is the 8-H proton. With that information, assign the spectum for the starting material and the spectrum for the product by placing the number of the carbon bearing the protons giving rise to the signal by the signal in the spectrum. When you are done, each signal in the proton NMR spectrum below should have a number (1-10). Please note that each signal (except for the SH one mentioned above) integrates for two protons. You should ignore any fine coupling you see. For example, treat the signal at 2.62 ppm in the product spectrum as a triplet. (10 points) b. Explain why the peak at 3.7 ppm in the starting material moves to 4.2 ppm in the product. Please restrict your answer to one sentence. (5 points) Came/5 m 62wa it w ablaze 66% W5 W 0983944 morsels/lam w,+tx0lmwlr13- c. Consider the triplet for the SH proton at 1.6 ppm. What does the coupling pattern and the sharpness of this peak tell you about the rate of proton exchange in this sample? Keep in mind that alcohol, acid, and SH protons often show broad peaks in a proton NMR. Please restrict your answer to no more than one sentence. (5 points) 1+ Wear/rs line We cog ~8KW8® is 5150.). (p0 oval/rage mums as $514 Prom 546de M W m WUW‘MW =7 DO WOWNg, M) d. Draw a splitting tree for the signal at 2.75 ppm. Again, please ignore the small fine coupling. How does this splitting tree allow you to identify which protons give rise to this signal relative to the protons that give rise to the signal at 2.62 ppm. Please restrict your answer to one sentence. (5 points) 71w mfifigflwe is W got/é +0 Mnee 0mm which Wfi TE Wufié ‘06 @057 W (QMBWQQWWW) e. What does the chemical shift of the protons on the carbon bearing the sulfur tell you about the electronegativity of sulfur relative to that of oxygen? Again, only one sentence. (5 points) 10 7. a. Draw an orbital diagram that explains why pyridine is a much better nucleophile than pyrrole. (5 points) I \ “@7111; km pyridine pyrrole pa} I" H b. 4-N,N-dimethylaminopyridine (DMAP) is often used to catalyze acyl transfer reactions. For example note the reaction illustrated below. Why is DMAP a better nucleophile than pyridine? Please restrict your answer to no more than one sentence and an appropriate drawing. (5 points) Me\N,Me O O i+ RNH 0 \ 2 “afl‘o’takoa + | / —> “L. 1NI \ KANE N / N Me Na2003 '1‘ I DMAP Me > I wmaaawl WM C) Jk"/\\I W 4,0,4 5 WE‘W’W In W c. Why does DMAP attack the carbonyl at gndm not C3? Pleagr rict your answer \néngJ-g to no more than one sentence and a drawing. (5 (points) fifag (MWthOfiealabmflQ 699% 50¢ ‘05 two mam d. Why does formation of the intermediate in the brackets, activate the carbonyl for nucleopilic attack more than the mixed anhydride does? Again, no more than one sentence.( (Spoints) fiWfii-GOW _W (01 a}: W 5%HW7SW W MIG Mm (mg? +0 WWQ) 11 a. Knowing that the pKa for a thiol (RSH) is approximately 10, the pKa for the protons alpha to a ketone are approximately 20, and the pka for methanol is approximately 16, calculate equilibrium constants for the two reactions illustrated below. (5 points) . 1; lob RSH + MeO'Na+ 1% ‘ + + MeOH O‘Na+ 2:3,bt’l O [:5 + (MeOH —— i: + MeO'Na” b. Write a “curved-arrow” mechanism for the following reaction. (5 points) Mag/R}. b L: Rsfij c. Keeping your answer to part a of this question in mind, why is sodium methoxide an excellent choice of a base catalyst for this reaction. (5 points) mgfiurrmw 4n @1474 W®W% W a) Wm armpmat. a $3wa WW5 M4 mm a. Circle the molecule below that would undergo the fastest Eg-elimination reaction. (5 points) H H O W0 Br Br b. Use an orbital picture to explain your choice in part a. (5 points) 12 c. Draw an orbital energy diagram for the radical illustrated below. (5 points) V 4 ,_ _ 2 4, ' 'V' ’(0 tow ”(a ‘1 11! O/\o ”’60) ‘37 Q?) m @223 d. Is the radical in part c of this question aromatic? Why or why not? Please restrict your answer to no more than one sentence and a drawing if you think it would be helpful. (5 points) m M 08 W Egg WM ‘% Wow W V? 90;) 4 W” m its aegwo “39(60va W @0me e. How can the following two molecules be differentiated using 13C-NMFl spectroscopy? (5 points) ...
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