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322af05_e3_key-1

322af05_e3_key-1 - CHEMISTRY 322aL/325aL Please M— EXAM...

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Unformatted text preview: CHEMISTRY 322aL/325aL Please M— EXAM NO. 3 L Print ast Name OCTOBER 26, 2005 First Name USC ID No. TA's Name Grader (1) (15) __ __ Lab Day & Time (2) (20) __ __ (3) (20) __ __ (4) (15) __ ___ (5) (10) __ __ (6) (10) __ _ (7) (10) __ __ (100) first letter of last name I will observe all the rules of Academic Integrity while taking this exam. Chemistry 322a / 325a _ - Exam No. 3 3 5 0k / (1) (15) Complete the chemical reactions below by providing the missing organic product or products within each box. You do not need to Show the byproducts of the reactions, or any mechanisms. Be careful to show stereochemical details in the products wherever they are important. Identify products produced as a racemic form. 2% C (A) H/ I \CH3 + CH31 CH2CH20- Na+ (100% ee) 9H5 6: CH3 (100% ee) Name acetoru'trile (B) H20 acetone CH3 (C) H’Ci\C1 + CH3S- Na acetonitrile CH2CH2BI (100% ee) C5H118X note a halogen (I ‘ atom remains (D) ' I l ’0 Br single stereoisomer (100% ee) 7H14O as two separable products provide stereochemical details (E) CH3CH2cHBr + Na+ 'CEN CH3 100% ee (R) /H' Mt— L \\ M acetonitrile SlJ \ C H N ’p/ f S) 71/ complete :tgzgeqstructure A042 Mr 6 “1L M of product {a . (,0 WC: H7 - = I“ Chemistry 322a / 325a Name -3- :2)? 519% M Mf mow/a CM!“ all) M65). (A) (10 Indicate whether each of the following compounds is chiral or achiral on the line below each one. oH (CH3)2CHCEC1CH3 CH2=CHCH2COOH C6H5CCH2c1-ltH3 L _C_h_u:e.l_ M C la ,‘ E$ 3 C6H5CH2CH2C1 2-cyclohexen-1-ol G-Lt" V PaL l Ck} v.4 (B) (10) Identify each pair of structures below as enantiomers, diastereomers, or the same stereoisomer on the line below each pair. Sums. 5&3 fiction: r- gOOH COOH Ifrl“OH PP’é‘VOH HVC \OH C . K/ O: l HC’ l \H ( ) H7 E“OH Hv’§‘~0H [::j /J‘\y/’ CH3 5H3 d?g§+°“0~\vl~3 (P ita. ‘l-thcoNc-S I TH lH3 Hl—OH Wl—OH CH3 CHH axe. “+1: 0 W 0:; Chemistry 322a /325a -4- Name Exam No. 3 aflg’h (3) (20) Circle the answer that correctly completes each question or statement below. (A) The equatorial stereoisomer will be most dominant in the equilibrium below in which of the following alkylcyclohexanes? (circle answer below) ___.. methycyclohexane <—— ethylcyclohexane iso . ro - 1c clohexane R t-butylcyclohexane (B) The number of stereoisomers of 1,3-dimethylcyclobutane is (circle answer) 1 @ 3 4 (C) The number of stereoisomers of 2,5-dichloro-3—methyl-6-pheny1heptane (shown below) is (circle answer below) ’I' v— ¥- 8. c6H5qHCHCICH2cH HCICH3 4 8 32 CH3 CH3 (D) Optically pure (100% ee) (5)-glyceraldehyde has a specific rotation of [(110 = -8.7°. A sample of glyceraldehyde that shows a specific rotation of +0.870 is a mixture of (circle answer) 10% R / 90% 5 45% R / 55% S 55% R / 45% S 90% R / 10% S (E) If someone gives you a sample of a racemic form of (+,-)—2,3—butanediol (structure is shown), this sample contains (cirecle answer below) HQ QH -only the meso diastereomer. CH3CHCHCH3 - R stereois 2,3—butanediol -a 50—50 mixture of the 5,5 and R,R stereoisomer -a mix ure 0 equa parts of the 5,5, R,R and 5,R stereoisomers. (F) In the reaction below that proceeds by an 5N2 mechanism, the initial rate of disappearance of R-X is rate = 0.0100 M'ls'l when [R—X] = [Nuf] =0.100 M. At [R—X] = 0.100 M and [Nuz'] = 0.0500 M, the initial rate of disappearance of R-X will be (circle answer below) 5 2 R-X + Nu? R R-Nu + X:' 0-00100 MJSJ 0.0100 M134 0.01500 M'ls'1 Chemistry 322a / 325a -5- Name Exam N o. 3 (3) Contd. 1 a] (G) The order of reactivity (fastest to slowest) of the alkyl bromides below in the reaction with sodium cyanide in acetone that follows second-order kinetics is R-CN + NaBr acetone (circle answer below) (FH3 I>II>III I>III>II CH Cl-LCHqCH Br CH Br CH CH Br 3 " h 2 3 3EH3 2 III>I>II I II III (H) The stability order (most stable to least stable) of the carbocations below is R-Br + NaCN + + + (circle answer below) CH3CH2CCH3 CHZCH2§HCH3 CH3CHCHCH3 I>II>III CH3 CH3 CH3 I II III H>I>III III>I>II (I) The order of reactivity of the halide ions in 5N2 reactions X + R-Y R-X + Y- follows the order F ' > C1 ' > Br' > I ' , under which of the following reaction conditions? (circle answer below) in probe solvents in polar aprotic solvents in the gas phase only II I and III I II III (J) Which of the following features are characteristic of the 5N1 mechanism for nucleophilic substitution? (circle answer below) inversion at a reacting stereocenter I I and III racemization of 10090 ee substrates II II and IV I and IV no dependence of the rate on [Nu: '] III second-order rate expression IV Chemistry 322a / 325a -6- Name Exam No. 3 (4) (15) Answer the questions below about the nucleophilic substitution reactions of 100% ee (S)—2-bromobutane. (A) (8) When a mixture of 100% cc (S)-2-bromobutane and a racemic form of sodium 2- butoxide in a racemic form of 2-butanol is heated, a nucleophilic substitution reaction occurs by the 5N2 mechanism producing two separable ether products. QFNa+ 5N2 9H3 93—13 CH3CH2CHBrCH3 + CH3CH2CHCH3 CH3CH2CHOCHCH2CH3 2—butanol di-sec-butyl ether 100% ee (5) racemic form (as two separable products) In the box to the left below, complete the stereostructure for (S)-2-bromobutane. In the box to the right below, complete the stereostructures for the two ether products (A and B). In the small circles below each stereocenter, indicate whether the stereocenter is R or S. On the line below each ether structure, inoi . te whether that ther prpduct ro . es plane- polarized light. ‘ , , (74 ‘ (B Will the ether products A and B necessarily be formed in equal amounts? Explain. NO ‘ Th‘j Ckr‘k Lcck§+‘ r4 0M1 ”5: ‘ The. ‘51-ka act 3 L; 'ath’KS +0 A awi \3 04". AQO$+‘¢"~°"‘"‘¢Q°J\Z “film we \cabgi ,—5 Mo"? <7\c~w\‘\"§6u~at~‘|kt\(7 m\&¥0d_ '(C) (4) The above reaction is carried out on a racemic form of 2—bromobutane (again using a racemic form of sodium 2—butoxide). How many separable products will be produced? @Two‘ Will any be optically active? Explain. Nor “A Mun &ELS+‘1MOML"\ Camk\v~u_\)‘\ s «5 out“ (@ APMJ TLL (”Fl/Vt“ Chiba—k d‘asfif‘tomoh \S ’hbho ?rD<lULei OL$ Co. T‘wkzmtg 74PM- Chemistry 322a / 325a -7- Name Exam No. 3 (5) (10) When tra115-4-chlorocyclohexanol reacts with KOH in aqueous acetone, the cyclic ether product shown below is formed. KOH HO ~ H C1 H20, acetone trm1s-4-chlorocyclohexanol Sketch a plausible mechanism that explains formation of the cyclic ether product from trans-4—chlorocyclohexanol using conformationally correct structures. Hint, start by drawing a chair conformation of trans-4-chlorocyclohexanol. Any key required conformational changes for the reaction must be explicitly shown. Also remember that the pI<a values of alcohols and water are very similar. H 09 “ c—es‘r e @ m ea: A c1 Kan | o H C H o <____, ‘ H (3‘ anouecuprxm +_ r; SN), mecamoxs % (CW THE Less vague BOB—\— C°NFOQMATLQM HUS\ BE RRKED ”Q Dub-5K 'T‘D RAGE [to—r174: HOLRQ‘UML 3'41 Rskcflow. M mf‘ (ay‘ A—N Chemistry 322a / 325a -8— Name Exam No. 3 (6) (10) The choice of solvent often has a dramatic effect on chemical reactions. Answer the following questions about solvent effects. (A) (5) t-Butyl chloride undergoes solvolysis in formic acid (HCOOH) and acetic acid (CH3COOH) to give t-butyl ester products as shown below. (CH3)3CC1 + Rc'OH RCOOH (R = H or CH3) t-butyl ester The solvolysis reaction proceeds 5000 times faster in formic acid (dielectric constant = 59) than in acetic acid (dielectric constant 2 6). Briefly explain this rate difference in terms of the mechanism of the reaction. ’musE 5°LN°U(SES PROCEED <37 THC: SN\ MECEKBKHSM. \ZDS G __.___—————§ § (CH—313C-C\ P.(eo H BCH335<® —\- Q\ pDR “VB—S SN\ THERE \S QDHS(DE [2.93.ch ek—KPRQE DFQELJDPHENT (N {:05 TS 0? WE RD: \N THE MORE. 90$KS°LUE§T 12"ch Atx : ILL: LEPDiué (7:3,: {1“, THE T34: SWU 9TH K \g W(qE SMALL-5K hé A-Nb LARéEL k 0 (B) (5) Dimethyl sulfide and methyl bromide react as shown below in an equilibrium reaction. Consider dimethylformamide (a polar aprotic solvent) and a mixture of water and methanol (a polar protic solvent mixture) as solvents for this reaction. Both solvent systems have the same dielectric constant of 37. Yet, the Keq is much larger in aqueous methanol, i.e. the equilibrium is more to the right. Explain this solvent effect. gory-x SOLUEN'TS AQE EQMP‘LL. DLR'KZr—ShY-KE “ [ONK’7—\9\\6’ (30060:. guf ,5) THE pogPKQ-Rfixg Spun—HT, SA— gombud(>_ \g AHW fl STABictzimc wr—Ldemcg aw "FHE 3‘9 ms [ON STATE \3 LDL‘DE RED (H) {12:35 ENE—V167) LEPDHQB‘ To A Acme; PRQOP—RRLE Ag. F—OYL THE memos}, lemon {>~ LP‘szEL K201 Chemistry 3223 / 325a -9— Name Exam No. 3 (7) (10) Provide a reasonable synthesis of (S)-2-phenylheptane from (S)-1-bromo-3- phenylbutane, ethyne and methyl iodide using any needed reagents. Your synthetic scheme should be a series of steps where the reactants, reagents and products are shown for each step. Do not provide any mechanisms, but important stereochemical features of the structures must be shown. H H CH3“q ‘CHzCHzBr .......... .. CHfi‘CHZCHZCHZCHZCHB CeHs C6H5 T HC ECH + CH3I and a :w needed rea- ents. M NH C”) ® CH '1: HC—ECH °‘ 1 HCE 2N ————95 2 LP?- NH3)~31°C C o. HC—Cm‘g N QHSQEQH- ‘1 :1) P"- C\—\ 3c5_¢ a [4 I“; l {‘EI~33 Q 5‘: R $3 __> g H CH + C c: c- a. (C CH '2. R 3 E .. 3 CbHr‘ z ‘\ CH3. \ CH‘S‘J‘fzqfl ...
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