Spring 07 Exam 3 Key - CHEMISTRY 225 . TEST #3 1. (12) JUNE...

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Unformatted text preview: CHEMISTRY 225 . TEST #3 1. (12) JUNE 1, 2007 A 2. (18) NAME we w a v 7 3. (26) GOOD LUCK! 4. (09) USE MODELS!!! 5. (10) Atomic numbers: H l, C 6, N 7, O 8, S 16,C1=17, Br = 35 TOTAL (75) . (12 Points) CHIRAL MOLECULES. a. ( f 6) Consider the list of organic molecules below. Circle all chiral mole_cules;' " underline all achtral molecules. CH30HQCH2(I3=CHCH3 CH3 utylcycioheptylprodigio ' Org. Left. 2007, 9, 1851 b. ( I 6) The highly functionalized molecule below has been identified as a key intermediate in the total synthesis of spirangien A, a structurally complex antibiotic isolated from Somgm'um cellulosum. The synthesis of a portion of this molecule has been achieved recently by chemists in Germany [Tetrahedron Lett. 2007, 48, 2905]. 9H OH QH o QH OH T i .x 52* 96““) (2/ 5 CH3 CH3 CH3 0H CH3 CH3 CH3 Ls; ‘ o (3) Directly on the structural formula, label all stereogenic carbons with asterisks. o (1) Determine the total number of enantiomers of this compound. 2 i 2. 0 (2) Disregarding configuration at the double bonds, determine the total number of _, diasrereomers of this compound. You may leave your answer in exponential form. E 1 " . (18 Points) STEREOCHEMISTRY IN ORGANIC REACTIONS. a. ( 7’ 3) The following conversion using a chiral catalyst was developed recently by chemists in Japan [Tetrahedron Left. 2007, 48, 2989]. It produces a single stereoisorner in high enantiomeric purity. (if? chiral . @OHG) _" catalyst — l H .. (R)—stereoisomer - (3) Write a stereochemical formula for the (R)-stercoisomer that shows its abSolute . ' configuration clearly. You may use the symbol Ph (for phenyl) to represent the._-aromatic ring. : . 0(3) BONUS QUESTION! A different research group in Japan developed a'reflat'ed-reaction for the :' preparation of substituted cyclohexanones [Tetrahedron Left. 2007, 48', 309.3]:n Under Certain: '_ . - . ,- " conditions the cyclohexanone derivative was formed in high enantiomeric puritymflinexampleis. shown below. Determine the absolute configuration of the cyclic product I l ' - - O - chiral _ catalyst + (CH3CH2lzzn —" ans. {2’ "'CH20H3 b. ( f 4) Chemists at the University of South Dakota have developed a “green” method for the oxidation of aromatic compounds to alcohols [Tetrahedron Lett. 2007, 48, 3417]. An example of the strategy is shown below. Describe the stereochemical outcome of this reaction and briefly justify your answer. OH air, ra hite | CHZCHg ——g—p—-—+ QCHCHg (and otherproducts) 3}: mwvfwk am On; Lin-val vita: l'd“—‘l +0 v-CC-‘LC ’iifm éa-Gfiué f, a. \b-oduelw‘fl, a g.“ it. ,Ll-va Pm'.(_ “(in V10“: ‘l.o,.,~lr mac- 39°?liwal J JYL_ (Dvoflwcxl rial -\/_.qza Klm. eel—wad fimlaslevmr at in... ~ rt... led at glee»: “in: Q ‘19 a. vac_t'_.w’<._ wi'é‘l-V~t. fv’D ll“? an“: A 09 at ya: Lev-Aka. wixx‘luvt a J c. ( 2’ 7) As we will see later on in the course, terminal alkynes can be converted to cfs-alkenes by a set of sequential reactions. The process is depicted in generic form below. R\ /C|-_|3 R—CECH —-n- R—CEC—CH3 —» KC:C\ H H o (4) Suppose this same set of reactions were used for the synthesis of (R)-cz's-4-methyl~2- hexene. Deduce the structures of the terminal alkyne reactant and internal alkyne intermediate that would produce an enanriomerically pure alkene product. - (3) Consider the trans-isomer to the right. Determine the stjcrcochemical relationship between the trans-isomer and (R)-cr‘s-4— _ _ I. - _. _;,methy1_2_h'exene. Circle all that apply. 4 i isomers ' J iaster‘eomers II .Enantiomers - _ _' Rotational isomers II ( f 4) Chemists in India have recently completed the total synthesis of the anti-2' tubercular agent erogorgiaene [Tetrahedron Lett. 2007, 48, 2841]. o (3) The first step in the synthesis was a catalytic hydrogenation of an unsatIirated ester (equation below). Write the structure of the product of this reaction with due attention to stereochemistry. H30 H2, catalyst ‘ I \\ COZCHg (3H3 - (1) The chiral aldehyde to the right was produced in a H3O ;/ O subsequent step in this synthetic sequence. Which term l\ l accurately describes the stereochemical relationship between : TH this compound and the original unsaturated ester (circle one)? (5H3 ame Ive configuration pposite configuration Inverted configuration 4 3. (26 Points) STEREOCHEMICAL FORMULAS. L-Serine, structure below, was used as a chiral starting material in a recent synthesis of compounds related to the biologically active molecule shikimic acid [Tetrahedron Lett. 2007, 48, 3512]. a. [ I 18) Using the templates provided, complete the stereochemical formulas for L— serine and its enantiomer D-serine. | _ l "x C H | t" H 3’ COgH lit/“r H 02 5 cozH \ \ H j Ho/Y H I C—CHZOH fl £591 —H' HCCHzf—WL '. / NH E ‘ 2 .. a CHZOH H filmKl H - " OH I L-serme ‘ H co H /M&z 9702“ Cili H\ H ' N 2 ' : HO 5 HOCHg—C..l N )6; -‘I _ . . 1 .l i I I. . N”? \‘H . CH20H ' H - H " ' = D-serine ' _ I N _ I ' I I OH b. ' r’ 3) The solubility of L-seri'ne is'5.0 g per 100 ml of water. Estimate the soliibility' ' . ‘Qf D_-_serine in water. Briefly justify your prediction}? I I __ _ _. I I Hm _ I I 'Tlét 4e 1/; D ~ "Le? “51:42: If A l; v .fllfl /('b0 m L" ééanL GMA "bu g'fialpfwe— (1 Va omaetllowew. 71+ mefiw‘iu'Q Cit/l omamllro Max, are ‘iAawifigg‘l maker-=- gmeapmreti lo? 61. ot‘qaei ‘lvé‘i, “wh- wALu "H;- LMDIP‘L Mel-u,m\7 “Die (L elxwal LA 0. ( :3) a (3) Determine the absolute configurations of L-serine. and D-serinc o (l) The specific rotation, [0L]33, .. for L-serine is -6.8°. Is L—serine dcxtrorotatory or levorotatory circle one)? o (1) What about its enantiomer, D-serine? (Circle one) de trorotatory ‘ vorotatory Impossible to determine from the information given 5 4. (09 Points) STILL MORE STEREOCHEMISTRY! a. ( x’ 4) Write structural formulas for a chiral and an achira! secondary alkyl brOmide each with the molecular formula CqusBr. ' “V w my achiral RX chiral RX GHAA fem/é b. ( f 5) 3,4—Dimethylhexane (Test #2) has two stereogenic carbons and can exist in three stereoisomeric forms. 0 (3) Using the sawhor5e framework below, write a stereochemical formula for the achiml stereoisomer of 3,4-dimethylhexane. HINT: there’s a plane of symmetry and the stereogenic carbons have been shown. 0 (2) Using any appropriate stereochemical formula, write a structure for a chiral structure! isomer of 3,4-dimethylhexane ' ' - ' chiral structural isomer 5. (10 Points) MULTIPLE CHOICE. Write the letter of the most correct response in the space provided to the left of the question. & The conversion to the right was utilized by . . . , i H 0.. o o H c“ 0 Chinese chemlsts 1n the course of a synthesrs of 3 3 '- V . . 1 ' —b- a certain cyclic sugars [Tetrahedron Lett. 2007, " / I. / 48, 3093} What term best describes the I HO CH3002" stereochemical outcome at the reaction site? ~ A. Retention B. Inversion C. Racemization D. Impossible to determine Q Which statement is always true? A. All diastereomers are stereoisorneric. B. All stereoisomers are enantiomeric. C. All diastereomers are geometric isomers. D. All stereoisomers are structural isomers. 6 D Which structure below corresponds to the enantiomer of the amino acid to the right? OH I 3 Hi|N\ H PH; C|>Ha .-C Moo '0 WC“ HgN‘ 1 “COZH /C 2H H3c/ “cozy. H / COZH A. H B. H30 0. D. HzN @ The specific rotation ([0L]D) of (R)-3-hexanol is -7.2°. A sample of 3-hexanol from the stockroom was found to have rotation of -4° under the same conditions. Determine the stereoisomeric composition of this sample. A. Enantiomerically pure (R)—3-hexanol B. Enantiomeric excess of (R)-3-hexanol C. Enantiomeric excess of (S)-3-hexanol D. Enantiomerically pure (S)—3-hexanol [J Which group would be assigned the highest priority by the Cahn-Ingold—Prelog system? A. ‘CH2CI B. —CHO C. —CO;H D. —C(CH3)3 ...
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Spring 07 Exam 3 Key - CHEMISTRY 225 . TEST #3 1. (12) JUNE...

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