Spring 06 Exam 4 Key - CHEMISTRY 225 TEST #4 JUNE 9, 2006...

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 2
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 4
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 6
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: CHEMISTRY 225 TEST #4 JUNE 9, 2006 NAME My! Useful atomic numbers: H =1, C = 6,N = 7, O = 8, Si = 14, Cl=17, Br: 35 GOOD LUCK! TOTAL 1. (25 Points) STEREOCHEMISTRY IN CYCLIC AND ACYCLIC MOLECULES. a. ( f 12) Chemists in Barcelona, Spain have recently succeeded in synthesizing the two enantiomers of the novel amino acid 3- chloroleucine [Tetrahedron Lett. 2006, 47, 3701]. The structure of one of these two enantiomers is Show to the right in jagged line format. _S_,3_5_) - (4) Determine the absolute configurations at the two stereogenic carbons of 3-chloroleucine. ( 2 o (4) Convert the molecule to a Fischer projection with C(]) at the top. a (4) Write Fischer projections for the enantiomer and a diastereomer of this molecule. CH(CH3)2 original molecute the enantiomer (Us; a diastereomer (25) .W(13) (23) (14) (75) 2 b. ( f 8) Deoxyribose, structure below, is the sugar component of DNA. 0 (3) Cyclic sugars are often depicted by means of a Haworth projection in which the structure is viewed edge—on. Complete the Haworth projection of deoxyribose by adding groups and hydrogen atoms in the appropriate locations on the structure. OH O OH 7’ Ho“ a (5) From the menu of structures below select the letter of the molecule that matches the description. A letter may be used more than once or not at all. OH (pH (pH OH oH ' O OH 0 . or . o ' o Y HO.__( \l. \/ WINCH HOV VOH \. fill i"\ . _ I“-__iii i gt i I‘ if "OH OH Ho“ "oa HO/ A B c D E —an alternate representation of dcoxyribose, -the enantiomer of deoxyribose b -a structural isomer of deoxyribose Q -two diastereomers ofdeoxyribose C _ and c. ( i’ 5) You may recall from Test #3 that 2,3-butanediol can exist in three stereoisomeric forms. A structure for the meso H3? H (optically inactive) form of 2,3-butanediol is shown to the right. I; C ,tOH - (2) Convert mesa-2,3-butanediol to a Fischer projection. H: \ _ HO o (3) Write jagged Zineformuias for the two optically active forms of CH3 i 2g3-butanedio]_ 5 mesa—2,3ubutanediol ‘I-t- I A 0H 5a optically active stereoisomers Fischer projection 3 2. (13 Points) CONFORMATIONAL ANALYSIS AND CYCLIC COMPOUNDS. 3. ( f 6) I (5) Write the two interconverting chair conformations of trans-1 -isopropyl~4-methylcylohexane. o (1) Circle the more stable conformation. b. ( f 7) The highly substituted cyclohexane derivative pinitol (planar projection formula to the right) was used as a chiral building block for a recent synthesis of the anticancer drug (+)-pancratistatin [Tetrahedron Lea. 2006, 47, 3707]. II (3) Convert pinitol to a chair conformation. C(2) has been identified and l H the methoxy group has been added to get you started. 0 (4) Write planar projection formulas for a chiral diastereomer and an aehz‘rar’ diastereomer of pinitol a. ( f 6) A chemist in Ztirich has found that (IE, 23)~cispentacin is an effective chiral catalyst in certain organic reactions [Tetrahedron Lea. 2006, 47, 3843]. The gross structure of cispentacin (IUPAC name 2- aminocyclopentanecarboxylic acid) is shown to the right. 2-aminocyclo- pentane carboxylic acid o (4) Write a stereochemical formula for (IR, 2S)-ci5pentacin that shows its stereochemistry clearly. I» (2) Determine the absolute configurations at the Z stereogenic carbons of the enamz’omer of (IR, ZS-cispentacin. (1 .6 , 2 ) 4 b. ( r’ 9) Mucocin, a natural product isolated from the leaves of Rollinfa mucosa, has been shown to exhibit extremely selective inhibitory effects against certain types of lung cancer and pancreatic cancer. The total synthesis of (~)—mucocin has recently been achieved by chemists at the University of North Carolina [Org Lea. 2006, 8, 23 69]. The structure of («)- mucocin is reproduced below. (-)—mucocin CH3 0 (3) Label all stereogenic carbons of (-)-mucocin with asterisks. One stereogenic carbon [C(4)] has been identified for you. - ( 1) Determine the total number of diasrereomers q of (~)—mucocin. You may leave your answer in exponential form. 2 - Za o (2) Directly on the structure of (-)-mucocin write in a pair of diastereotopfc hydro gens and label them H3 and Hb. - (3) Suppose the configuration at C(4) were inverted. Speculate on the impact of this molecular change impact on the prOperties of (-)-mucocin and justify your answer. I“V-(V"lcm ask/1 COM u Wyalioc.‘ @ C(91) womlgl Fu-o/‘luflf. 6L A\C($vlf(\wuu~_2v E35,) CQ—Mucochw. fl; wasiltwgfi TL“? altayltawcmww- wcmlcl (aerqc 2—»- all U‘t’é aria-i Rw’“wfilvl7)“l-90 vwfg til—L99- ws-wlel La drills vtw'i. c. ( f 4) The complex tetracyclic molecule 10- deacetylbaccatin Ill served as the starting material for the synthesis of a structural analogue of docetaxel a compound used for the treatment of breast and ovarian cancer [Org Lea. 2006, 8, 2301]. The structure of lO-deacetylbaccatin III is shown to the right. 0 (3) Locate and identify two sources of strain in 10- deacetylbaccatin HI. Be specific. “ i gut shift AWLL L“)! “UL é‘lva‘f w/ +‘C-vé‘thal glfltg __ o (1) Directly on the structural formula of 10-deacetylbaccatin III locate the bicyclo[5.3.1]undecene skeleton. 5 d. ( f 4) Chemists at Pennsylvania State University have recentlydescribed a synthetic approach to cylindricine B, a tricyclic marine alkaloid isolated from Cfaveh'na cylindrich off the coast of Tasmania [Tetrahedron Lett. 2006, 47, 3815]. The structure of cylindricine B is shown to the right. - (2) Directly on the structure highlight the two rings that are joined by a Spirocyclic ring junction. ‘ cylindricine B J o (1) Identify the location of the hexyl group I "EH—— '. - axial gauche - (Circle one) o (1) Describe the structural relationship of the hexyl group and H3: trans- E- Z- 0 (3) BONUS QUESTION! Would you identify the nitrogen of cylindricine B as a stereogenic ’2 9 h . a v atom. Whyorwhytiot. Y”; '4 9 a filyvivj hfipalow. 1+ 9 lacy—clad 443 - uv clf+F{vm.-l have»er ti ’Dv—L {LL-grwl‘b ml— \fwd— oft-v Q [\l etc a Iijur. Nova. Vii-L. raft-mil.) - N Claw. LauL. Qtflay fl )Lus‘c Cowifluva lieu; 4. (14 Points) MULTIPLE CHOICE. Write the letter of the most correct reSponse in the Space provided to the left of the question. ' 2 Chemists in Taiwan have recently developed a OH OH synthetic route to the two terpenoid natural products to the right [Org Lett. 2006, 8, 2217]. What term best describes 3 . . . .,,OH OH the structural or stereochemlcal relationship between them? and O, A. Structural (constitutional) isomers . : . CH3 CH3 B. Conformational isomers C. Enantiomers D. Diastereomers i___m__u ,2 An enantioselective synthesis of (~)-quinic acid, a natural product that HQ C02H has a regulating role in the biosynthesis of aromatic compounds, has been 7 deveIOped by Canadian chemists [Org Left. 2006, 8, 2035]. The structure of (—)-quinic acid is shown to the right. Determine the total number of equatorfa! substituents in the more stable chair conformation of (-)-quinic HO ; acid. [ OH A. Two B. Three C. Four D. Five (-)-quinic acid g 6 A. 0 kcalfmole B. 3 koali’mole C. ll kcali’mole D. 88 kcali’mole Estimate the energy barrier separating the two interconverting chair conformations of cyclohexane. Lg Which cycloalkane is correctly associated with its most stable conformation? A. CyCIOpropane: envelope B. Cyclobutane: puckered C. Cyclopentarie: fully planar D. Cyclohexane: boat D What is the principal source of strain in the conformation of methylcyclohexane in which the methyl group is axial? A. Angle strain B. Torsional strain C. Bond length strain D. Transannular strain 0 A “O” The compound to the right was the immediate precursor to (-)-quinic acid I in the synthesis cited on p. 5. What term best describes this compound? 0 A. Bridged bicyclic compound B. Bridged tricyclic compound 3 C. cis~fused bicyclic compound D. trans-fused bicyclic compound BF C/ Which of the following molecules can exist in meso form? Br CH3 | Eir A. CH3CHQCHCH20H3 a. Q o. C/ D. CHacHZCHfiZHCHg | CH3 Br CH3 ...
View Full Document

Page1 / 6

Spring 06 Exam 4 Key - CHEMISTRY 225 TEST #4 JUNE 9, 2006...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online