Exam1Key - EXAMINATION 1 Chemistry SB\u Name M SID Print...

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Unformatted text preview: EXAMINATION 1 Chemistry SB \u/ ' Name: M SID #: Print fir name before second! Use capital letters! GSI (if you are taking Chem 38L): Peter Vollhardt October 2, 2008 Please provide the following information if applicable.- Making up an 1 Grade (if you are, please indicate the semester during which you took previous Chem SB: Semester instructor Please write the answer you wish to be graded in the spaces provided. Do scratch work on the back of the pages. This test should have 20 numbered pages. Check to make sure that you have received a complete exam. A good piece of advice: Read carefully over the questions (at least twice); make sure that you understand exactly what is being asked; avoid sloppy structures or phrases. It is better to be pedantic in accuracy now than sorry later! Good Luck! DO NOT WRITE IN THIS SPACE l. ___ (30) ll. __ (30) m. _,___fl (50) Iv. _______ (50) v. ____ (30) Vi. __ (so) vu. (20) Total: __ (250) 2 |. [30 Points] Name or draw, as appropriate, the following molecules according to the IUPAC ruies. indicate stereochemistry where necessary (cis, trans, R, or 8). Br 0. (S)-3-Methylcyclohexanone d. trans—4-Bromo-2—oxo-3-butenal ll. [30 Points] Compound A undergoes preferential eiectrophiiic attack by E+ to give only one of the three products shown. OCH3 OCH3 OCH3 OCH3 N02 N02 N02 i E E+ ? or or E E CH3 CH3 CH3 A t] D E Which one? Mark the box below your choice with an X. Write the resonance forms of the intermediate formed on attack of E+ on A at: xi mix Emiratesonance forms no2 Three resonance forms flew“ 'iéhree resonance forms Circle (in your answers above) the most strongly contributing resonance forms of the attack at 0—3, GS. and 0—6. Considering all ofthe above most strongiy contributing resonance forms, which one is the best overall? Redraw it in the box beiow. iii. [50 Points] Add the missing components (starting materials, reagents. or products) of the foilowing reactions in the boxes provided. Show stereochemistry when appropriate. Aqueous work-up (when required) is assumed to be part of a step. it is not part of any answer. 3- CHSOH (solvent) 0 O -—"-—" \ // //S O Thermodynamic product b. CH3 hv -—-—> CH3 0. O + o -——-» CH3 CH3 CH3 NBr Product of ring opening M W. HOCHZCHEOH —---——-——-l-— IR spectrum of product: loo lanLHlnLt-lxl 4033 3mm EUDU LEN LUUU {WU WENUHI EH I III CH30 Brg, FeBrg ——--———-—-,-— CI Monobromination IV. [60 Points] An attempt to effect allyiic bromination of A generated the unknown B. The complete spectral data for this product are shown below in the sequence: 1. H NMR, 2. 13c: NMR, 3. Mass, 4. IR, 5. UV. 0 O H + NBr ———~—-—> B(Unknown) H300 A O a. After consideration of the spectral data, write the structure of the product in the box below. ’l. 1H NMR Spectrum (for expanded section, see bottom spectrum), HEP—454335 ppm 2H ix,— eU .0 ppm 10 11 b. Draw again your suggestion for the unknown in the box and label the hydrogens A, B, C and D giving rise to the corresponding signals in the 1H NMR spectrum on p. 10. Consider resonance in your assignments of B and C. 2. 130 NMR Spectrum (these are six single tines). E 114.2 ppm '12 DEPT spectra (don't worry if you don’t remember what that is) shows that the carbons giving rise to signals A, C, and E are attached to one hydrogen each Signal F is due to a carbon with 3 attached hydrogens. Signals B and D are associated with carbons without any bound hydrogens. Draw again your suggestion for the unknown in the box below and label the types of carbon atoms A—F giving rise to the corresponding signals in the 130 NMR spectrum on p. 11. For the assignments of B versus D and C versus E, consider the effect of electronegativity of the attached atom and the effect of resonance, respectively. 13 3. Mass spectrum Atomic weights of all the elements in the reaction on p. 9: H 1; C ‘12; N 14; O 16, Br 79 and 81 (1:1 isotope ratio). Caution: Not all of these elements are incorporated in the product. 100 QB 81] 70 BI] 140 1513 4D 50 ED '30 ElEl 90 ‘1 DE] 11D 12D 130 NE a. Clearly mark on the spectrum the molecular ion as “ll/1+" and the base peak as "8*? b. in the box above the fragment ion m/z = 135, indicate the structure of this fragment. 4. IR Spectrum Transmittance 2500 2000 1500 1080 Warrenurnber (cm—1} 3500 3000 Confirm the presence or absence (circle one) of the following bonds. Enter an approximate expected stretching frequency in the box. «fink V (Cspzu—H) is: {ésej} absent at 17 (Cspg—H) is: present] absent at <f§opo cm'1 7: (C20) is: @ absent at Magi“? Cm" '14 5. UV spectrum Place an X mark into the box next to the most accurate statement. The spectrum depicts a nonconjugated compound. The spectrum is that of a colored compound. The firm is at 300 nm. E The unknown is aromatic. 15 V. [30 Points] Write detailed stepwise mechanisms for the following transformations. Use only structures and "arrow—pushing" techniques. Note: These are n_ot synthetic problems. Do not a_ql_cl any reagents! What you see is what you have! Work from left to right in the following spaces. There is much more space than you will need. NH2 0 Catalytic H+ ———-————————-————~b- 16 17 o )L O o O/\H —--———-—-—---—-—--—--——-———-—>-— Work from left to right in the foilowing spaces. There is much more space than you wiIE need. 9+ f) “5‘51"” M‘% o \ mg” : .. z H 9 WH-k v. ig/ Mr” I . H— “ f" Q 18 VI. [30 Points] Provide a reasonable synthetic route from starting material to product. Note: Several steps are required. and there may be more than one solution to the problem. Do not write mechanisms! Write out each step separately, including reagents and products. 3- CHEOH Caution: You cannot introduce the ~CH20H group directly. Hint: To do so, think alcohol synthesis. Work from left to right in the foltowing spaces. There is much more space than you will need. .19 b. Synthesize compound A from any acyclic materials containing six carbons or less. Hint: Think Diets—Alder reaction. Caution: Work backwards. What compound must precede A for a retro—Dieis—Alder step? H H \ ON ON A Work from left to right in the following spaces. There is much more space than you will need. ' mac/Ix} W & W a," E (a? W MN} :117” y? M 20 Vll. [20 Points] Place an X mark in the box next to the most accurate statement. a. The electron withdrawing pOWer of benzene substituents 1—4 decreases and their electron donating power increases in the order —CH3 ——OCH3 —F —-N02 1 2 3 4 D 1,2,3,4 4,3,1,2 D 4,2,3,1 D 4,1,2,3 b. Circle the compounds which are aromatic .0 The End J7 ...
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Exam1Key - EXAMINATION 1 Chemistry SB\u Name M SID Print...

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