Final Exam Key

Final Exam Key - CHEMISTRY 322aL/325aL Please a. FINAL EXAM...

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Unformatted text preview: CHEMISTRY 322aL/325aL Please a. FINAL EXAM Print Las Name DECEMBER 8, 2005 First Name USC ID TA's Name Grader (1) (45) __ (2) (20) __ Lab Day & Time (3) (20) (4) (15) (5) (30) (6) (15) __ __ (7) (15) (8) (15) (9) (25) ._ __ (200) first letter of last name I will observe all the rules of Academic Integrity while taking this exam. Chemistry 322aL/325aL -2- Name Final Exam 3 2 C A/ (1) (45) 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. Show or describe stereochemical details in the products wherever they are important, such as a racemic form of a chiral product. "Workup" means adding water and brinqing the solution to neutral pH. - excess NaNH2 liq, NH3, -33°C ’2. (A) CH3CHBrCHBrCH3 CH 3C -CCH 3 C4H6 H2 . C (B) R Pd/C ' (pmsoned atalyst) CM productdecolorizes Big/Ch L % JV fir N OEt a (C) CH3$CH2CH3 CH CZCHCH3 'CH3 ethanol 3 ( QH3 major product minor product both products decolorize Brz/ CC14 aw! m3? ——L*—-C°::f C1 ‘2 7 (H3 @ “‘3 C7H1L major product only (2H3 EH3 é + Na+ iCN t 'trile H' l \ CHZCHZBr “9 0‘“ CHZCH3 (100% ee) (E) HI? “ twice; N Chemistry 322aL/325aL -3- Name Final Exam A 3 a! C. (1) Contd. / H3C , (i) hot KMnO4, KOH, H20 F ( ) (ii) workup H3C (G) H\ _ /CH3 (i) 0504. pyridine CH3CH2 H NaHSO3, H20 L (H) l Q Q ‘CH-SQHI aiming CH2CH2CH3 \ (100% ee) Chemistry 322aL/325aL -4- Name Final Exam (1) Contd. (K) H ‘ 9H (ii) CH3I H36 (100% ee) (i) 3H3.THF/THF (L) E (ii) HZOZ/KQH, H20 ifl/OL‘J (AA/07 (i) Hg(OAc)2/THF,HZO ‘\ 1 (M) .. CH3 q M N BH ,N OH f} ‘4 CH3 (11) a 4 3 OH 0 d(‘ product shows strong band 1 in ir near 3400 cm" ( )H\R_f/ H3 + Na*"OCI-I2CH CH;QHZO CHZQIQ H O 1% J6; o 9H3 ? CH3502C1 (O) Ho’fi\H amine base ‘ CHZCHZCéHS 3 6 UAW 2 (1000/0 88) Chemistry 322aL/325aL -5- Name Final Exam (2) (20) Answer the questions below. (A) (5) All valence-level non-bonding electrons are shown in the structures below. Add any missing formal charges immediately next to the atom on which they reside. 1 MC A CH3CH2'é'H CH3CH2CHzfig-l3 CHZCH3 CH3 file :9: H-§-H CH3§$H CH3CH2c-c-H H H H (B) (6) Provide detailed structures inside the boxes for the following compounds. All stereochernical details must be clearly shown and identify stereocenters with an asterisk (*). CC—Hs H *CHcch H 3 (E)-4—methyl-2-hexene s. ~ «L M W W W W 6 MythQCyclohexan-lfll /_——- (C) (9) Provide complete names that correctly identify the stereoisomers of 2,3- dibromobutane on the lines below the following structures. 3,3-dimethylcyclohexanol o B BS: f H l; 5'“ PM. CH3|u... _ --u||| Hm... _ “NHL Hull \u 3 9‘ ’44 H’ \CH3 CH3] \CH3\ CH3 H % “’4‘” “A B c (S S)’2$-i§bnno— S ~2'S-(Lfl3m 0.. Ql~23~cklammo ~ W hrs—Lunak ‘ Erth Which of the above stereoisomers (A, B or C) will rotate plane-polarized light? A 4" C— Which of the above stereoisomers (A, B or C) constitute the chiral diastereomer? A +C Which of the above stereoisomers (A, B or C) constitute the meso diastereomer? B A ' Chemistry 322aL/325aL ‘ -6- Name Final Exam (3) (20) Answer the questions below. (A) (10) Indicate whether the following pairs of structures represent the same compound, or whether they are related as enantiomers, diastereomers or constitutional isomers. ._\_u H3 H3 H OH H OH Br B CH CHzCI-I3 3 H H €M6-wh‘bm1r3 g‘ngax-Vt owl 1:: oOOH $OOH H | OH HO—l—H H%7-OH HO“T_‘H COOH COOH (B) (10) Circle the more stable isomeric structure in each pair below. (E)-2_pentene 1,2-dimethy1cyclopentene OI‘ or 3,4-dimethylcyclopentene (Z)-2—pentene (CH3)2CH L'nerrustry azzaL/ 325m. -7- Name Final Exam (4) (15) The 1H NMR spectra of three constitutional isomers of C4H7C10 are shown below. Assign structures to these spectra from among the choices in the box below by drawing the selected structures inside the boxes to the left of the spectra. Correlate the structures with the spectra by drawing arrows from the groups of equivalent H in the structures to the resonances in the spectra. structure choices 9 (CI-I3)2CHCC1 CH3CHC1 CH3 CH3CH2CH2CC1 ClCHZCHZCCH3 CH3CH2CHC1CH Chemistry 322aL/ 325aL -8- AName Final Exam ;l_4éaaj (5) (30) Circle the correct answer for each statement or question below. (A) The correct molecular formula and U-number (degrees of unsaturation) of the structure below are (circle answer below) HZCH3 / \ C6H50 2U C6H80 2U O C6HBO 3U C6H90 3U (B) The numbers of valence electrons in the ionic structures below are + circle answer belo ) Cw W I II I 13, II is} I 13, II 16 (C) The order of acid strength (strongest to weakest) of the following compounds is (circle answer below) CH3CH20H CH3COOI—I HC ECH CH3NH2 II>I>IV>III I II III IV II>IV>I>III II>III>I>IV ( II>I>III>IV ' (D) The lowest energy conformation of trans-1,2-dimethylcyclohexane is (circle answer below) H3 H3 H H CH3 CH3 H H H H3 H3 (E) Among the Newman projection formulas of 2,3-dichlorobutane shown below, identify the meso diastereomer and the stereoisomers of the chiral diastereomer. Cl (:1 C1 H\ H3 CH3\ H CH H CH3 CH3 CH3 H C1 Cl C1 I II III (circle answer below) I is th m o and II and III are the chiral diastereomer. II is the meso, and I and III are the chiral diastereomer. I IS t e meso, an I and II are t e c 1ra - iastereomer. I, II and III are all different conformations of the meso diastereomer. Chemistry 322aL/325aL -9- Final Exam Z (5) Contd. MK 4 (F) The reaction of propyl bromide with sodium ethoxide in ethanol yields products I and II, as shown below. The reaction mechanisms that produce these products are Name CH3CH2CHzBr + NaOEt CH3CH2CHZOEt + CH3CH=CH2 ethanol I H (circle answer below) Iby 5N1, II by El y 8N2, II by El I by 5N1, II by E2 (G) The reaction of t-butyl bromide in aqueous ethanol gives I and II, as shown below. The reaction mechanisms that produce these products are ‘?r (PR CH3$CH3 + (CH3)2C=CH2 CH3 H20, EtOI—I CH3 1 (R = H, Et) II (circle answer . lw Iby 5N2, II by E2 I by 5N2, II by El I by 3N1, II by E2 (H) The order of reactivity (fastest to slowest) of the alkenes below in the acid—catalyzed hydration reaction is + alkene + H20 HQO alcohol (circle answer below) M M W I>II>III I II III II>I>III III>I>II (I) The roton decou led 13C NMR 5 ectrum of a c cloalkene C H shows three P P P Y 6 10 resonances at 6 127.3, 8 24.5 and 5 22.1. Which of the following structures are consistent with this observation? (circle answer below) Q U DE A l I II III IV V I, II and IV I, IV and V (I) The mass spectrum of an alkane C7H16 shows prominent peaks at the masses 100 (M+ peak), 85, 57, and 43. Notably absent are masses at 71 and 29. Which alkane below is consistent with this result? CH3CH2CH2CH2CH2CH2CH3 CH3qHCHzCH2CH2CI-I3 (circle correct structure) CH3 9H3 CH3§CH2CH2CH3 CH3 Chemistry 322aL/325aL -10- Name Final Exam A 2 m (5) Contd. (K) A gaseous mixture of one mole each of cyclopentane (I) and ethane (II) undergoes photochlorination at 100°C to give a product mixture of chlorocyclopentane (80%) and chloroethane (20%). What is the ratio of the intrinsic reactivities of the H in I and II on a I per H basis : RI/Rn? 1 (:12 + CH3CH3 O hv, 100°C + CH3CH2C1 I II a mixture of one mole each 80% 20% RI (circle answer below) R“ = 4/1 2.8/1 1/2.4 (L) Which statement below correctly compares the reactivities and site—selectivities of the photochlorination and photobrornination reactions of alkanes? hotochlorination is faster and less site-selective. Photo romination is as er an more site se ec 1ve. Photochlorination is slower and more site selective. Photobromination is faster and less site selective. (M) Which of the following reactions of 1,2-dimethylcyclopentene are stereospecific anti- additions? (circle answer below) hydroboration catalytic H2 bromination epoxidation 1 and 111 111 and [V with peroxyacids I 11 III IV I, II and IV (N) Overall Markovnikov addition to an unsymmetrical alkene is observed in which of the following procedures or reactions? (circle answer below) hydroboration/ oxidation HI addition I H I, II, IV oxymercuration/ demercuration H+/ H20 III IV II and IV only II (0) The addition of ZnC12 accelerates the reaction of ROI-I with concentrated HCl. In these reactions, ZnC12 functions as (circle answer below) a Lewis base. a nucleophile. an electrophile. a polar aprotic solvent: Chemistry 322aL/ 325aL -11— Name Final Exam (6) (15) Answer the two questions below. (A) (7) The heats of hydrogenation of 2-methyl-1-butene (AI-1°: -28.25 kcal/mol) and 2- methyl-Z-butene (AH°= -26.68 kcal/mol) provide a quantitative measure of their relative stabilities. Show how this is possible by completing an energy diagram below showing . the reactant and product states. Provide detailed structural formulas of the reactants and , product in their proper states in the diagram. Illustrate how the diagram provides a measure of the relative stabilities of the alkenes. Add energy values to the Y-axis so your diagram is properly scaled in energy. In the box below, indicate which alkene is more stable and by how many kcal/mol. C“: m Mex—ear 3 4mm a - __ 9H3 cu cu. : C 0+; +H7_ relative enthalpy 99's Q-M¢+.\\g \a'): lou'l‘v‘hk l3 1 mm srh—loiL to; \.5‘1 tau/m Chemistry 322aL/325aL —12- Name Final Exam (6) Contd. (B) (8) The free energy diagram below describes the change in free energy for the multi-step process: In the diagram below, show 240 the locations of A, B and C. Z (ii) the locations of all transition states (TS). 7/(iii) the energy difference for the free energy of activation (AG)F ) of the rate-determining step. Also label the RDS. progress of reaction What does the Hammond-Leffler postulate say about the transition state for step 1, A-) B? STQP \ \5 \'\\5\r\\-( (“AQVSO’IxCQ (NRA OCCU (‘5 05h!— CL\0’V\3 'l—kk WOUL‘HOK Coos—filtmgj‘ve, 'Pkg TS 4—Or S‘Hv\ $69117 V'TLSQnAlAleS B M\ s-h—uc‘l-ui‘L Chemistry 322aL/325aL -13- Name Final Exam (7) (15) The addition of HBr to isobutene (2—methyl-1-propene) in the presence of peroxides (ROOR) gives an anti-Markovnikov addition product by a free radical chain mechanism. (A) (2) Write a chemical equation that describes the overall addition reaction by providing the missing reactant and product states below. CH3 H =CHZ b HBr Pe‘OXides mac—cesz CH (B) (4) The free radical chain mechanism must be initiated. Provide chemical equations for the initiation steps below. Circle and identify the chain carrier that is produced by the initiation steps. CH RO—OR ——; 1R0- (C) (6) Provide below chemical equations for the two propagating steps, (i) and (ii). Circle all the chain carriers in these steps. Using values of homolytic bond dissociation energies, D(A-B), provided in the Appendix, calculate the enthalpy changes for the two propagating steps. Place your answers in the boxes. CH3) ‘qg AHO for step (ii) (D) (3) Explain riefly why the anti-Mari” 3dition product is formed and not the Markovnikov addition product. The Mom s-‘n—Valg «\\<\!\ T‘s-ACCL‘ \'t\+thw<1(\‘~*k K3 H :- mo L CH3Q _c Hie F 5:31"; C‘qu C High 8“; CH3 ‘» CH C=CH + B; 0“ ems-r- macaw:ch 3 Z 8" ' producw ‘ Chemistry 322aL /325aL -14— Name Final Exam (8) (15) Answer the following questions. (A) (8) The oxymercuration reaction of an unsymmetrical alkene is highly regioselective. Sketch a mechanism for this reaction with 1-butene. Use the curved arrow formalism. Clearly identify and circle the key intermediate. In the text box below, explain the key factor that controls the regiochernistry in this reaction. (CH3CH2CH=CH2 + HggAcb HZOITHF “smirk 2‘ Hfiofiq ‘- (E‘Ai ) Do not include the demercuration reaction in your mechanism. Et- A \OrKA \‘K? \lczQ/\ $3M Ciu MarcjrC—ntum H 9 H Mac“ (4 KOM L.)a.'l~¢ r‘ orb-t-chS ‘Fkt fixer-1 (\QC‘H‘D" Post—bulk Coke-born Mm c._ 4A aka—m pk: K451 Fgm5~9 PQ’K\'\A3 (go. L+§OW\\ l ueo 9“ H ? E‘bfficHLHSOAQ “” 3 H r wfi o (>1 NMQ (at; Sitj‘; —- CHZHSO AC \7\ (B) (7) The reaction of trans-Z-butene by the two step procedure of (i) epoxidation with a peroxyacid (RCO3H) , and (ii) hydrolysis in aqueous acid produces mesa-1,2-butanediol. Sketch mechanisms for (i) and (ii). Clearly indicate the stereochemical modes of the key steps in (i) and (ii) that lead to the overall stereospecificity of the hydroxylation procedure. (i) epoxidation HQ (PH CH3CHCHCH3 (ii) H3O+, H20 /\/ H1680 Chemistry 322aL/325aL -15— Name Final Exam (9) (25) A Table of Reagents is provided in the Appendix for your use in designing the three requested syntheses below: (A), (B) and (C). Each step in a synthesis must be a separate chemical equation showing reagents and products. Mechanisms are not required. (A) (5) Provide a short synthesis of 2,2,3,3-tetrarnethyloxirane from 2,3—dimethy1butane. Chemistry 322aL/325aL -16- Name Final Exam (9) Contd. (C) (10) You are an organic chemist working for a pharmaceutical company. You have been assigned the task of preparing the stereoisomer of di-(3-methylpentyl) ether shown below (I). You have in your laboratory the optically pure enantiomers of 3-methyl-1- pentene previously prepared and resolved by one of your co-workers. First, assign R/S labels to the stereocenters on the lines below the structures. CHsCHf'VCl \CH=CH2 CH3 5— e 2‘ 100% ee , t ' \ + ~ - ' ' ' ‘ " CH3CH2 E K q CHZCH3 C H H3 E S I H2C=CH7§H\H2CH3 di-(3—methylpentyl) ether E_3 (as a single stereoisomer shown above) H3 Provide below an efficient and plausible synthesis of I from the starting materials. Will I rotate plane-polarized light? N 0‘ t'i' is. Mag 0 \—\ {4 g c a (9) T'H-FBH; TH?— E €\~f3QH CH 1 ) Hz01)¥-Ot+' H20 CHSCH’I CH 2 3 t2 , ,_ u (C‘QH (i)THF.BH>,IH\= E C.”- CH 1c “3 Hzoz‘KoT’xth trtocwa?!‘ ‘QWLCHX 3 CH3 M if it E (H 50254 (C N 0 I \ C o M c I Curse”; O‘HB 92w; H AN“ gas ( CfichC\93 H LC H10 gaff—K ...
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This note was uploaded on 05/22/2008 for the course CHEM 322AL taught by Professor Jung during the Fall '07 term at USC.

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Final Exam Key - CHEMISTRY 322aL/325aL Please a. FINAL EXAM...

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