322af02_e4_blank - CHEMISTRY 322aL EXAM NO 4 Please Print...

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Unformatted text preview: CHEMISTRY 322aL EXAM NO. 4 November 20, 2002 Please _________________ Print Last Name _________________ First Name SSN ______________ Grader ______ ______ ______ ______ ______ ______ TA's Name____________ Lab Day & Time_________ (1) (30) _____ (2) (15) _____ (3) (15) _____ (4) (20) _____ (5) (10) _____ (6) (10) _____ (100) first letter of last name I will observe all the rules of Academic Integrity while taking this exam. _______________________________ Chemistry 322aL/325aL Exam No. 4 -2- Name_____________ (1) (30) Complete the chemical reactions below by providing the organic product or products (as requested) within each box. You do not need to show byproducts of the reactions or any mechanisms. Provide stereochemical details in the products wherever they are important. "Workup' means adding water and bringing the solution to neutral pH. CH3 Na + -OCH2 CH3 CH3CH2 OH, heat (A) CH CHCH CH CH Br 3 2 2 2 Major product decolorizes cold aqueous KMnO4 solution. OH CH3CH2 CH2CCH3 (B) CH3 conc. H2SO 4 heat Two products C5 H10. Label major and minor products. (C) CHBrCH2Br 2 eq. NaI acetone Product decolorizes Br2 /CCl4 CH3 (D) (i) conc. H2 SO4 (ii) H2 O Product does not decolorize Br2/CCl4, but is soluble in cold conc. H2SO4. Chemistry 322aL/325aL Exam No. 4 (1) Contd. -3- Name_____________ CH2 C (E) CH excess H2 Pt Product does not decolorize Br2/CCl4 . (F) CH3C=CH 2 CH3 + HI (G) CH3 CH3 + Br2 H2 O C7 H13BrO CH3CH2 (H) C=C H CH2CH3 H + CH2N 2 heat or irradiation ethyl ether C7 H14. Does not decolorize Br2 /CCl4 . (I) =C(CH3)2 KMnO4 , HO-, heat H2 O isolable product C6 H10O Second product is soluble in water and is lost. CH3 CH3CH2 CHCH=CH2 (J) (i) OsO4 , pyridine (ii) NaHSO3, H 2O Product is soluble in cold, conc. H2SO 4. Chemistry 322aL/325aL Exam No. 4 (2) (15) Answer the questions below. -4- Name_____________ (A) (3) Provide a detailed structural formula for the compound below inside the box (E)-1-chloro-2-methyl-1-pentene (B) (4) Indicate the number of degrees of unsaturation ("U" number) for each compound below. Place your answer on the line below each structure. CH3 O CCH 2CCH3 = CH3 C (C) (6) How many different proton resonances (signals) would appear in the 1H NMR spectrum of each compound below? Ignore spin-spin interactions. O CH3 CH3 CH2 COCCH3 CH3 CH3 CH2 C=C CH3 H H = CH3 CHOCH2 CH3 CH3 (D) (2) A proton resonance appears at d 5.0 in an 1H NMR spectrum recorded using a 200 MHz spectrometer. What is the chemical shift of this resonance in Hz relative to tetramethylsilane as a reference signal? Place your answer in the box. chemical shift in Hz Chemistry 322aL/325aL Exam No. 4 -5- Name_____________ (3) (15) On the reagent shelf in your lab, you have samples of the diastereomers trans- and cis-1-bromo-4-tert-butylcyclohexane. Unfortunately, the labels have fallen off. You decide to use your knowledge of organic chemistry to identify them. You react each sample with sodium ethoxide in ethanol. You observe one sample yields 4-tert-butylcyclohexene very rapidly, while the other sample only slowly produces this same product. (A) (2) In the labeled boxes below draw the lower energy chair conformation for each diastereomer, as requested. Hint: the tert-butyl group is much larger than the bromine atom. trans-1-bromo-4-tert-butylcyclohexane cis-1-bromo-4-tert-butylcyclohexane (B) (10) Which diastereomer reacts faster with sodium ethoxide in ethanol? Provide a mechanism that explains why this reaction proceeds smoothly with this diastereomer. Be careful to show stereochemical details in your structures. What favorable stereochemical features in the faster reacting diastereomer promote a fast reaction with sodium ethoxide? (C)(3) Briefly explain why this same reaction is so slow with the other diastereomer. Chemistry 322aL/325aL Exam No. 4 -6- Name_____________ (4) (20) Circle the answer that correctly completes each question or statement below. (A) The more stable alkenes in the three pairs below are CH3 CH3 (CH3 )2C=CH 2 CH3 CH2 CH=CH2 A B AAA A AAB B BAB BBA A B (circle answer) (B) The order of acidity (strongest to weakest) of the compounds below is (circle answer) CH3 CH2 CH3 I CH3 C II CH CH3 CH2 OH III NH3 IV III>IV>II>I III>II>IV>I III>II>I>IV IV>III>II>I (C) Compound A has the molecular formula C21H34O2 and does not contain a triple bond. Catalytic hydrogenation yields a compound C21H38O2. This information indicates that compound A contains -two double bonds and three rings. -three double bonds and two rings. -four double bonds and one ring. -two double bonds and no rings. (D) The order of reactivity (fastest to slowest) of the alcohols below in the acidcatalyzed dehydration reaction is OH OH CH3 CH2 CH2 CH2 CH2 OH CH3 CCH2CH 3 CH3 CHCH2CH 2CH 3 CH3 III II I (circle answer) III>II>I I>II>III III>I>II II>III>I (E) Which of the following reactions of an alkene is a stereospecific antiaddition? (circle answer below) catalytic hydrogenation hydrohalogenation bromination hydroxylation Chemistry 322aL/325aL Exam No. 4 (4) Contd. -7- Name_____________ (F) When 2-bromo-2-methylbutane is heated with sodium ethoxide in ethanol, the expected alkene product mixture is CH3 CH3 CH2 C=CH2 I CH3 CH2 =CHCCH3 II CH3 CH3 CH=CCH3 III (circle answer below) III>II>I II>I>III III>I I>II (G) Which compounds below are not soluble in cold, concentrated sulfuric acid? OH Cl (circle answer) CH3 I II III IV I and II II and IV I, II and IV I and IV (H) Which of the nuclei below with nuclear spin quantum numbers of (I) will provide nmr spectra? 16 8O (I = 0) I 15 7 N (I = 1/2) II 7 3 Li (I = 3/2) III 12 6C (I = 0) IV (circle answer) I and II II and III I, II and III I, II, III and IV (I) Among the four compounds below, the one with the most upfield 1H NMR resonance is (circle your answer) CH4 CH3 Cl CH3 Br CH 3F (J) In the compound below, B C D A ClCH2 CH2 OCH2OCH3 the most downfield resonance in the 1H NMR spectrum will be from the hydrogens labeled (circle answer) A B C D Chemistry 322aL/325aL Exam No. 4 -8- Name_____________ (5) (10) Complete the synthetic scheme below by providing detailed structures of the missing compounds inside the boxes. Be careful to show stereochemical details wherever they are important. CH3 CH2 CH=CH2 Br2 CCl 4 (i) 3 equiv. NaNH2 (ii) workup, NH4Cl, H2 O (i) NaNH2 (ii) CH3 CH2 I C6H10 C4H6 Forms a black precipitate with AgNO3 in aqueous NH3. H2, Pd/C catalyst poisoned with amine KMnO4 , HOH2O, cold Product decolorizes Br2/CCl 4. C6H12O2 An achiral compound. Chemistry 322aL/325aL Exam No. 4 (6) (10) -9- Name_____________ (A) ) (5) Compound A, C6H12O, does not decolorize a solution of Br2 in CCl4. Compound A reacts with a hot concentrated solution of sulfuric acid to give an hydrocarbon (B) with the molecular formula C6H10. Compound B rapidly decolorizes a solution of Br2 in CCl4. Ozonolysis of compound B produces compound C which is the dialdehyde shown below. Provide structures for compounds A and B in the boxes below. hot conc. H2SO4 A, C6 H12O B, C6H10 (i) O3, CH 2Cl2 , -78oC (ii) Zn, H2O O O HCCH2CH 2CH 2CH 2CH = = C Chemistry 322aL/325aL Exam No. 4 (6) Contd. -10- Name_____________ (B) (5) The "annulenes" are a series of cyclic polyenes with alternating single and double bonds that display informative 1H nmr spectra. In the structure of the compound [18] annulene, shown below, there are two types of hydrogens, outer and inner. At reduced temperature, the 1H nmr spectrum consists of two resonances at d 9.3 (more downfield) and d -3.0 (more upfield). Ho Ho Ho Ho Ho Ho Hi Ho Ho Ho Ho Ho Ho [18] annulene Hi Hi Hi Hi At -60oC, the 1 H nmr spectrum of [18] annulene shows two resonances at d 9.3 and d -3.0. Hi Offer an explanation for the two very different chemical shifts and assign the observed resonances to the Ho and Hi hydrogens. Hint: Look at the annulene as a "super benzene ring." Draw a picture to illustrate your explanation. ...
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