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322af06_e3_key - CHEMISTRY 322aL/325aL Please KC EXAM NO. 3...

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Unformatted text preview: CHEMISTRY 322aL/325aL Please KC EXAM NO. 3 Print Last ame OCTOBER 25, 2006 First Name First 4 digits of USC ID No. _ _ _ _-XXXX-XX TA‘s Name Grader (1) (15) __ __ Lab Day a: Time <2) (20) .__ <3) <20) __ <4) (15) :__ (5) (20> __ <6) (10> __ (100) first letter of last name I will observe all the rules of Academic Integrity While taking this exam. Chemisz 322a / 325a -2~ Name Exam No. 3 ——— 3 ml» (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. (i) NaNHZ, liq. NH3, -33°C (ii) (R)-1-bromo—3-methylpentane (A) CHgCECH complete the stereostructure above for the product H20 (B) acetone H3C\ CH3 (100% ee) , H 7/ 4L Br (C) (31%ij + CH3s' Na+ H ‘ ‘0 H acetonitrile (— 9" (“'9’ I “L C8H16S asasingle product CH3 : \ heat (D) CH3CH2CHK$ Br CH OH CH2CH3 3 (100% ee) CH3 (E) {$‘C1 + Nach acetone CHZCHZBr 50:13; C (100% ee) y haloge Chemistry 322a/ 325a -3- Name Exam No. 3 (2) (20) Answer the questions below. (A) (5) Identify each of the following compounds as chir or ach'ral on the 1' e below each structure or name. M M‘IL M ‘ two ( ‘ x. CH3CH2CHC1CH=CH2 CHquilCHzCI-Ia 3—brom0pentane M CH3 Qkfva.\ C fivoc: Q¢£3EL\ Br A) 6} OH Ck 3 Eu» \ (kc/k3 ms (B) (10) Identify each of the following pairs of structures as enantiomers, diastereomers, or the same tereoisomer on the lines below the pairs. 1 M ~\\\CH3 C:H3 C:H2CH3 M\Br 31"?» CHzCH3 CH3 '1 $0351 §fi15m§omer ‘3q5j3:a.°m¢t§ A (2R,3R)-2,3-dibromobutane \ C1 CH3 CH3 1 and and (28,3S)-2,3-dibromobutane M C6H5 COOH , c1 anqnftomem‘ dlgs‘l’kriomlfis Mm...“ (C) (5) Provide complete IUPAC names for the two structures below on the lines below the structures. Your name must correctly provide all the stereochemical information in the structures. Q 3 H H ‘\\\H CH3V§VBr CH2CH(CH3)2 “I my 9 m ‘1‘“BT‘OMO rub“ L r“ MK "fir:$‘ 3- In “A150 L) V Chemistry 322a / 325a ~4- Nam Exam No. 3 a ‘WZ/ (3) (20) Circle the answer that correctly completes each statement or question below. (A) Halostachine (structure shown) is a natural product found as the (R) enantiomer in rye and fescue grasses. A 100% cc sample of the (R) compound shows [a] = -47.00 at 20°C in ethanol. A sample of halostachine that shows a specific rotation of -23.5° when measured under the same conditions is a mixture of (circle answer below) H MHCI'E 50% (R)/50% (S) 60% (R) /40% (S) CeHs O 0 o 0 0 halostachine 100°/o ee (R) [a] = 47.00 75 /° (RV25 /° (5) 0 /° (RVZO /° (5) (B) The stability order (most stable to least stable) of the three stereoisomers of 1,2- dimethylcyclohexane shown below is (circle answer below) H3 H H3 I II 111 ‘ H CH3 H > > H H3 3 H 11>111>1 I>III>II (C) Consider structures I through IV below. What is the relationship between I and IV and what is the relationship between II and IV? H H (3H 9H I II III IV I /I recon itutional isomers and II/IV are enantiomers. I /IV are diastereomers and I IV nantiomers. /IV are enantiomers and II/IV are enantiomers. I /IV are constitutional isomers and II/IV are diastereomers. (circle answer) (D) The Fischer formulas among I, II and III that are the same stereoisomer as Fischer formula A is or are H3 H2CH3 H3 H CH3 OH CHZCH3 CHZCH3 A I II , III (circle answer) I and II II and 111 only II Chemistry 322a/ 325a -5- Name Exam No.3 2‘ 4 (3) Contd. (E) Among the four stereoisomers of 3-chloro-2-pentanol listed below, the enantiomeric pairs are CH3CH2CHC1CH(OH)CH3 (circle answer below) (25,35)-3-chloro-2-pentanol (2S,3R)—3-chloro-2-pentanol 1/11 and III/IV I II I/III and II/IV (2R,BS)-3-chloro-2-pentanol (2R,3R)-3-chloro-2-pentanol III IV only I and IV, II and III are diastereomers (F) The reaction of a primary alkyl bromide (RBr) with hydroxide ion proceeds by an 5N2 mechanism in aqueous acetone at 25°C with a rate constant of k = 0.0100 M'1 s'l. What is the initial rate of the reaction at [RBr] 2 [HO'] = 0.100 M? (circle answer) Rate = 1.00 M s‘1 1.00 x 10'1 M s'1 1.00 x 10'3 M 5‘1 1.00 x 10'4 M s'1 (G) The reactivity order (fastest to slowest) of the alkyl bromides below in an 5N2 reaction is (circle answer below) H3 gr CHggCHZBr CH3CH2CH2 HCH3 CH3CH2CH2CH2CH2Br 111>1>11 H3 I 11 In I>II>III II>I>III (H) The rate of the reaction of 100% ee (S)-1-bromo-1-phenylethane with sodium methoxide in methanol (shown below) conforms to the rate expression rate = k[RBr]. The mechanism and stereochemical outcome of this reaction are §CH3 r (S) C6H5CFHCH3 + NaOCH3 C6H5 HCH3 (100% ee) (circle answer) SNZ/ inversion 5N2 / racemization 5N1 / inversion 5N1 / racernization (1) According to Transition State Theory, the magnitude of the rate constant (k) for a chemical reaction depends on (circle answer) AGO AHO TASO (I) According to the Hammond-Leffler postulate, the structure in the transition state for the rate-determining step of a typical highly endergonic 5N1 reaction of R—X will 'rcle correct statement below -have considerable ionic characte . —resemble the starting -X compound. —show Very little bond heterolysis. -show considerable bond homolysis. methanol Chemistry 322a / 325a -6- Name Exam No. 3 (4) (15) Answer the following questions. (A) (9) Provide the missing conformational structures inside the boxes below for the chair to chair interconversion of cyclohexane showing the hydrogens labeled H A and H3 in the structures. Sketch the change in potential energy as these conformational changes occur using the energy diagram below. Draw arrows to show where the structures inside the boxes belong on the energy diagram. chair 1 half chair "pure" boat kcal / mo] 10 re tive potential energ conformational change (B) (2) Draw the most stable conformational structure of cis-1,3-di-t-butylcyclohexane (CH inside the box to the right. *i (C) (4) The most stable conformational structure of trans-1,3-di-t-butylcyclohexane is a boat. Draw the most stable "pure" boat conformation in the box below. Explain this observation. H_ h.)\\Z\L ‘HfiLF’xfl‘S \m-H‘strg s-tmtrm anf‘fi\[ r’Y\ 5— $OQ+ CGm‘FDy-WHOM COW?%PLA @Nt‘r Com-ém‘ k 4—\-L Qvlrxosuh Corvqfan-‘r-tox 0‘? Mmfi 4.3—le -t-'\1 U‘biqgQ(D Li‘smmk Plates cL-E-—lou+)l§r°-JP 3'11 ‘3“ch T“+V‘°AVUS Monk 54‘th QWNV 4A,.“ QT); Box“. Chemistry 322a / 325a -7- Name Exam No. 3 (5) (20) Answer the following questions about the nucleophilic substitution reaction of 2- bromobutane that yields 2-butanol. (THF, tetrahydrofuran, is an ether co-solvent to improve the solubility of the organic compounds). (PH CH3CH2CHBrCH3 + NaOH W CH3CH2CHCH3 + NaBr When 100% ee (S)~2—bromobutane ([OL] = +2310) reacts in the presence of 0.2 M NaOH in aqueous THF as solvent, the product is 100% ee 2—butanol with [a] = -13.5°. (A) (2) Complete the stereostructure of (S)-2~bromobutane in the box to the right. ° F aviurqa \aqz‘t‘ (B) (1) WhiCh f—‘narffiomerpf 2'bUtan01 (C) (1) What is the Hughes-Ingold notation 15 forme‘i 1“ thls reaCtlonr for the mechanism of this reaction? (5) or (R)? g E a The specific rotation of the 2-butanol produced in the reaction with 100% ee (S)— 2-bromobutane depends on the presence or absence of NaOH, as illustrated in the table to the right. [NaOI—I], M [on] of 2-butanol 0.2 -13.5° 0.050 —6.75° 0.000 0° (D) (2) Based on the results in the table, what terms describe the stereochemical outcome of the reaction at [NaOI—I] = 0.2 M? hut-4‘3! D ’1" At 0.000 M? ram V\\’J_k"'r1 o m (E) (4) Briefly explain why the stereochemical outcome depends on the concentration of NaOH. No calculations are needed, but refer to a comprehensive rate expression that incorporates competing mechanisms of reaction in explaining the stereochemical outcome. 2~$x~ome \sv’tn—n 1’ u. 31c unchuq &\\<1\ ro MCA 1' ML7 Ruck \o*-\ W TM (“M9 V‘Kkl- my V K PM“ “*(arz'vsi 0M t _ ‘ mm : kl [(2433 4— R1013? Lfiol A-F \“ (“o-‘1, +\~L SNL VA! u¥o~9gfi Aow‘thcdff‘ A-t— low (W‘llor \"‘r\ «0.505%?ka 0"? «441.4 +\,\K SN\ wgkuaq sw\ AOMkmqflrtS- (F) (2) Calculate the percentage of each competing mechanism of reaction at [NaOI-l] = 0.050 M using the stereochemical outcome shown in the table. .01 5° '1 l o O __ x - M. CH5}: o,ol;oM‘ I},Q:.~t..‘l§°_ Tkkflamz “vs-SD Box,- Tk‘as' Boy. 04 VOW Aug+ Oubrsgzs'gom 6.x [Mth—Ssx O’K “*AQSM Q‘Ad SOD/p (Rumwéc 4‘9,st Ctr-«~34; (Lek +\\¢\ Suck- Chemistry 322a / 325a -8- Name Exam No. 3 (5) Contd. (G) (8) In the box below, identify the operating mechanism (by Hughes-Ingold notation) for the reaction of (S)-2—bromobutane in aqueous THF with no added M NaOH. Sketch this mechanism that explains the stereochemical outcome of an optically inactive product. Your mechanism must show all the bond breaking and bond making steps using the curved arrow formalism. Identify the rate-determining step and clearly identify the key intermediate. Clearly show the chemical steps that show how the reaction of the key intermediate leads to the stereochemical outcome. A urfl’cro\~(31 S H 1 D5 ‘ Hughes-Ingold m § 0 6 notatlon CH’} 2’ 3 (Q Caz—bocc‘c‘rom ‘(J—me‘hrw Liaj‘ K «c rm} ‘rL l—l E} H ® ® / H~Ct> ‘ 3Ql®p£>fl+ 2’ E’fiOH “5‘0" / < - 1.3+ 13" H r +— ’I ‘9 C C C“; L 3 L L (kw-pa.) CkQV'A oxow‘om (ewckm‘l Flac¥i0’v\ oil‘oomnjm IDM® 9°..ka mfg cur-k "new!" M \M‘s ¢S ,— (CEU RX H a. A Q / +\ ® \«l—fi ‘* “GS Whigs EL? {+30 —\~ \Wc&,m£u H H qr 3 ® 3 CH3 F M @ VPhQ-K—H ()st \ (N H mama ’LEH’J” #325“ i” 9—H gag Hao 4*“ y/\C”DH So '. 80 A Kagmmx‘g Far M Chemistry 322a / 325a -9- Name Exam No. 3 (6) (10) Propose a plausible synthesis of 5-methy1-1-phenylhexane from 1-bromo—2- phenylethane and any other needed organic compounds with any needed reagents. C6H5CH2CH2BI' + — - - — - - - - - ~ — - - -> C6H5CH2CH2CH2CH2CH(CH3)2 any needed reagents Your proposed synthesis should start With the starting materials and proceed to the product in a series of steps. Reagents and products must be shown for each step. Mechanisms do not need to be shown. } Z \ CH3 \’£ u (EH C“ a ,\ HC-ELC‘Q"(\ Yuk» z 643 ® Q>\—\ m we GuszECH ~°‘——*=> QH QHQEC‘. m. Lrfi ‘EBOQ 3‘ 3 ’ QH3 @ CHfiHCE c: A? C”: re NH3,~3?°L CH3 ...
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322af06_e3_key - CHEMISTRY 322aL/325aL Please KC EXAM NO. 3...

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