CEM 252, Fall 2018 Midterm Exam 3, Version A Wednesday, 14 November, 2018, 6:00 PM Room 138, Chemistry Name (print) Signature Student # Key

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1 CEM 252, Fall 2018 Midterm Exam 3, Version A Wednesday, 14 November, 2018, 6:00 PM Room 138, Chemistry Name (print) Signature Student # Key Version Section Number (-2 pts if you don t know this) A Feed it right, mechanical pet And then get behind the wheel Put a little starch* in the old Corvette ooh, smooth moving steel (Led Zeppelin) *Glucose polymer 1(40 pts) 2(20 pts) 3(20 pts) 4(20 pts) 5 Bonus* (4 pts) *To earn bonus question points, you must have fully answered the other four TTAL (100 pts) Score Note: Be sure to look over all the questions first before beginning the exam Below are section numbers and times Recitation Day and Time # Room Instructors M 8:00 AM - 8:50 AM 1 Room 109 Chem Bldg Monique Noel M 9:10 AM - 10:00 AM 8 Room 323 Chem Bldg Monique Noel M 11:30 AM - 12:20 PM 4 Room 183 Chem Bldg Benjamin Appiagyei M 11:30 AM - 12:20 PM 6 Room 109 Chem Bldg Monique Noel W 8:00 AM - 8:50 AM 2 Room 127 Chem Bldg Yuting Zhou W 9:10 AM - 10:00AM 11 Room 323 Chem Bldg Yuting Zhou W 1:50 PM - 2:40 PM 3 Room 183 Chem Bldg Benjamin Appiagyei W 1:50 PM - 2:40 PM 12 Room 085 Chem Bldg Yuting Zhou Th 4:10 PM - 5:00 PM 9 Room 126 Chem Bldg Benjamin Appiagyei F 8:00 AM - 8:50 AM 10 Room 110 Chem Bldg Reza Ghazfar F 9:10 AM - 10:00 AM 5 Room 085 Chem Bldg Reza Ghazfar F 3:00 PM - 3:50 PM 7 Room 110 Chem Bldg Reza Ghazfar

2 1 (40 pts) Multiple choice questions; 4 pts each; please bubble in your answers on the multiple choice sheet: i (4 pts) For fructose, a ketohexose (shown in its Fischer projection at right), how many stereoisomers (including fructose itself) are possible? ii 0 a 4 b 6 c 7 d 8 a C b C c C d C C C (4 pts) Which of the following aldaric acids is meso (ie achiral)? C 2 C 2 C C iii (4 pts) Which of the following combinations would lose water to form the enamine shown at right? a N b 2 c d N N N N Enamine iv (4 pts) Which of the following compounds is a reducing sugar? a C b c C 3 C 2 C 2 C 2 d v (4 pts) Which of the carbonyl compounds below is the strongest acid at the indicated C- site? a b c d

3 vi (4 pts) Which of the Fischer projections of pentoses below represents the ring opened form of the a-d-ribofuranose shown at right: a (A) b (B) c (C) d (D),, C 2 C 2 C 2 C 2 vii viii ix (4 pts) Which two of pentoses A-D above in question vi would form the same aldotetrose upon Wohl degradation? : a [A and B] b [A and D] c [B and C] d [B and D] (4 pts) Which pair of the carbonyl compounds A-D below would come from retro aldol cleavage of the 4-hydroxy-5- methylhexan-2-one shown at right? A B C D r a [A and B] b [C and D] c [B and D] d [A and C] (4 pts) Which of the carbon nucleophiles below is a bad Nu: candidate for reaction with methyl vinyl ketone via Michael addition (AKA 1,4- or conjugate addition, as shown at right)? 4-hydroxy-5-methylhexan-2-one a b Ph Ph c d N EtMgBr Me 2 CuLi x (4 pts) Which of the resonance structures below represents a different enolate anion than the other three a b c d

4 2 (20 pts) Carbohydrate reactions and stereochemistry: i Complete the mechanism below by filling in the provided boxes (4 pts each) with intermediates, charges and arrows for the formation of methyl β-d-glucopyranoside (Notice that by this point in the course, we no longer explicitly include lone electron pairs on each oxygen; you should be able to recognize where they appear As we have often said about groups, if including the lone pairs helps you write the mechanism steps, go ahead and draw them in) E C 3 ( C 3 " "i In " C 3 i s C 3 C 3 - methyl β-d-glucopyranoside ii (4 pts) Consider methyl β-d-glucopyranoside, the end product shown above Draw its a anomer as a chair structure in the box below ' ii! cus iii (2 pts) What is the chemical formula of methyl β-d-glucopyranoside? Ct I 406 iv (2 pts) What is the configuration (R or S) at the C1 carbon (ie the anomeric carbon) of methyl β-d-glucopyranoside? R anomeric (C1) carbon C 3 methyl β-d-glucopyranoside

5 , ' 3 (20 pts) Reactions: i 1) LDA/-78 C 2) C 3 C= 3) 3 I on ii 1) xs Br 2 /Na 2) 3 C BB iii 1) NaEt 2) 3) 3 /heat -4 IIE iv C C 2 N 3 / 2 heat " o - : C C v 1) PBr 3/Br 2 2) 2 Br

6 4 (20 pts) Mechanisms and synthesis: i (10 pts) Provide a detailed arrow pushing mechanism for Reaction 1 below The three steps are: (1) proton transfer; (2) nucleophilic attack; (3) proton transfer Show the steps (2 pts each) and the two intermediates formed along the way (2 pts each) Reaction 1 NaEt Et Reaction 2 3 / 2 heat Reaction 1 mechanism: Et 9 Na step 1 step 3 - o ~ o p - A Et Eton step 2 Eo ok ii (2 pts) In the last step of Reaction 2, C 2 is lost, forming an enol, which tautomerizes into the final stable diketone product shown Please draw this enol in the box at right XLt iii (8 pts) Complete the syntheses at right with reagents from the lab bench below Each box gets a single letter answer A) Et 2 N C 3 CN E) MeMgBr Et 2 enol intermediate F B) C) D) 1 LiAl Et 2 CuLi 2 MeBr xs Et F) G) ) KCN/CN PPh 3 1 Me 2 CuLi 2 EtBr 5 (4 pts) Write a limerick on the back of this page about something chemical that we've learned in class since last exam ere's the rhythm & rhyme: With Fischer pix you needn't guess Put C= at the top and don't stress Carbons' tail like a kite With an - at right Shows that center is R and not S E C B Me Et CN