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Spring 10 Test 2 Key - CHEMISTRY 225 TEST#2 1(10 V 2(24...

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Unformatted text preview: CHEMISTRY 225 TEST #2 MAY 28, 2010 1. (10) , V 2. (24) NAME \A 9w it ~/ 3. (09) Some useful atomic numbers: H = l C = 6 N = 7 4. (18) O = 8 Cl = 17 Br = 35 5. (14) TOTAL (75) GOOD LUCK! l. (10 Points) ROTATIONAL ANALYSIS, AND EQUIVALENT CARBONS. a (___ / 6) Consider the sawhorse formula of 2- chloropentane H39 /CH2CH3 | (compound A) to the right. H...-C—C "'H a (4) Convert this molecule to a set 01 Newman projections showing the three cl: )4 staggered conformations looking down the C(2)- C(3) bond. compound A o (1) Circle the Newman projection in which the two alkyl groups are anti to each other. o (1) How many structural isomers with the molecular formula C5H10C12 can be derived from 2—chloropentane? 5 b. (__/4) 0 (2) Write a structural formula for an alkyne, C8H14, with fo_ur structurally unique carbons. O (2) Write a structural formula for an isomeric alkyne with seven structurally unique carbons. CBHM, four structurally unique C's CBHM, seven structurally unique C's 2 2. (24 Points) HIGHLIGHTS FROM THE CURRENT CHEMICAL LITERATURE! a. ( / 12) Each of the highly unsaturated fatty acids below has appeared in a recent scientific article. Answer the following questions about each compound. 0 (6) Below is a structural formula for juniperonic acid, a compound recently synthesized by Norwegian chemists [Tetrahedron Lett. 2010, 51, 2852]. A L / )juniperonic acid i l - Determine the molecular formula of juniperonic acid i ' 29 Li Z 2 Or, - How many signals will be found in the 13C NMR spectrum of juniperonic acid? 20 .«J - Locate all carbon-carbon bonds of juniperonic acid about which there will be restricted rotation. 0 Wig “3 5 o (2) As reported in the May 10, 2010 issue of Chemical & Engineering News researchers at Scripps Research Institute have found that stem cell differentiation can be regulated by controlling the reduction of stem cell metabolites. One such stem cell metabolite is shown to the right. Directly on the structural formula circle all carbon—carbon double bonds with the (Z)- configuration. O (4) To the right is a structural formula for another metabolite of an omega-3 fatty acid. As noted in the May 17, 2010 issue of Chemical & Engineering News, this and similar compounds may account for the beneficial effects of omega-3 fatty acids. _ - What is the total number of vinyl ic hydrogens in this compound? I O - Directly on the structural formula write in all allylic hydrogens. Label them as Ha. b. ( / 2) Chemists at the University of Mississippi have developed a method for converting aldehydes to unsaturated nitriles [Org Lett. 2010, 12, 2171. An example is shown below. The procedure affords high yields of the (Z)- isomer. Write a structure for the (Z)—product. (Z)-isomer 3 c. ( / 4) The readily available natural product citronellal (structure below) was used by Indian chemists as the reactant in a scandium catalyzed reaction sequence [Tetrahedron Lett. 2010, 51, 2963]. 0 (3) Complete the hydrogenation reaction of citronellal. 0 (l, BONUS QUESTION) Label all stereogenic carbons of citronellal with asterisks. 0' '3 H W H2, cata'YSt \ WU b _/7 (A 9k 0 citronellal ca o (3) Account for the fact that the 13 C NMR spectrum of citronellal shows ten lines rather than nine. HINT: Why are all carbons structurally unique? 11...“. -9 came 1L; Laura cod-Mir cu aQ, ({7)( owe no“- 4 “saw. a, x». (iii; :4 4 ML as.“ VV?-‘EI Mm,” “2:19 5:910 “A (0‘73 (canLou cit—a3, curl wtfl7 i L ‘ivautr tic Cilia (ow. U: caliber“... fl” Juana/J: 0mv u 0"? C‘V 6 ‘1‘.» UV“ ML €MVv‘/OU‘~ TL-evti—OVE) 0L ici‘ui ‘3" f0 wen—«e7ucvuixm‘iC—9) (O [twvl‘m 0 (3, BONUS QUESTION) (Jeraniol [(2E)- -3 ,7—dimethylocta— 2,6—dien-1-ol, oil of geraniums], is a structural isomer of citronellal. Write line formula for this compound that shows the geometry at all double bonds clearly. 99'3““ a d. ( /6) o (2) One of the reactants used in a recent study of coupling reactions H C 3 C UL O H involving alkynes was propargyl alcohol, C3H40 [Org Lett. 2010, 12, 2286]. Write a structural formula for propargyl alcohol. propargyl alcohol 0 (2) A structurally related compound, 2-decyn-l-ol, served as the starting material in a recent synthesis of the cyclic compound below, compound B [Tetrahedron Lett. 2101, 51, 3134]. Write a structure for 2-decyn-1-ol. O 2—decyn-1—ol H C7 Hi 5 C7H15 H compound B geometric isomer of B I (2) Reported in the same paper was the synthesis of the geometric isomer of compound B. Write a structure for this compound. 4 3. (09 Points) ACIDS, BASES, AND ORGANIC REACTIONS. a. ( / 6) Consider the acid—base equilibrium below which serves as the first mechanistic step in the synthesis of l-bromobutane from l-butanol. ® 9 CH3CH2CHZCH20H + HBr CH3CH2CH2CHZOH2 + Br @> A C34 C4; O (4) Label each species in the forward direction as acid (A), conjugate acid (CA), base (B), or conjugate base (CB). 0 (2) The equilibrium favors the species on the left-hand side. Identify the strongest acid in the reaction. Justify your choice briefly. m e w L l,V ; m V. 3” a «5 ac iri Lac, 9, veaciiou aiWA7‘. ”FVO’P‘TL‘ weair/c acic'i- Len—tr, lamr. it” in i9...) Law f.» in we AWL or was vwciaub» (LH'é') V14»? (over He" 1* ‘flx weaLLv 04:44 OVA Ogd/ZCAIZCLQCHC WUsv‘i’ Lt 11¢ 9H~ac (10313 b. ( / 3) Complete the following alkene reaction. 9v OE: HBr<g> flu? “L7 4. (18 Points) STRUCTURAL FORMULAS AND STRUCTURAL ISOMERISM. a. (_ / 6) Write structural formulas for all derivatives of cyclopentane having one methyl and one ethyl group as the only substituents. (All compounds will have thé‘flecular formula C8H16. ) Provide the systematic (IUPAC) name for one of the structures you have drawn. Be sure to indicate which structure you are naming. = . C49 . 132.0; «4117“? i a; a; UL or? cyclopentane derivatives i" ¢+L7i ' i~M€VrL7i€7¢ iOFPu‘I‘fi M1 5 b. ( / 5) Write structural formulas for all monochloro- derivatives of 2—methylbutane. (Ah, cu; c7”; ' i an? cunt, mg or; c.“ CH: CH; mace/(4 cu; t (Dig, C 8%; CtéC/t monochloro— derivatives c. ( / 7) Write structural formulas satisfying each of the following descriptions. 0“? QEQMQEQI; W a strain-free hydrocarbon a terminal alkene 2,3-dimethylcyclohexene 5. (14 Points) MULTIPLE CHOICE. Write the letter of the correct response in the space provided to the left of the question. There is only one correct answer per question. A Why would the compound to the right be identified as an unstable alkene? i A. There is virtually no overlap between the two Czp atomic orbitals forming the pi bond. B. Catalytic hydrogenation of this compound is highly endothermic. \ C. The four atoms surrounding the double bond are forced to be coplanar. D. There are two electrons in pi antibonding molecular orbital of this molecule. (D Consider the three isomeric molecules below. Which statement is true? . \ @CHzCHg C(V CHsCHzCECCHZCHZCH3 A. I and II are geometric isomers. B. H and III are geometric isomers. C. I and III are rotational isomers. D. I, II, and III are all structural isomers. C Which of the following best describes the C(2)—C(3) bond in vinylacetylene (structure to the right)? HZC=CH—CECH A. G[Csp3-Csp3] B. “[Cspz'Cszl C. “[Cspz'cspl vinyiacetylene D. O'lcsp'cspl 6 A A research team at UCLA has prepared [24] —dehydroannulene, a remarkable unsaturated cyclic hydrocarbon with the molecular formula C24Hg [Org Lett. 2010, 12, 2286]. The twenty—four carbons are arranged in a single large ring. Use the molecular formula to determine which set of unsaturated groups might be found in this compound? A. eight CEC, four C=C B. eight CEC, five C=C C. four CEC, eight C=C D. twenty-one C=C C Estimate the strain in the gauche conformation of butane. A. 66 kcal/mole B. 5 kcal/mole C. l kcal/mole D. 0 kcal/mole, the gauche conformation is unstrained. l; A pair of isomeric alkenes, compounds C and D, undergo Athdrog catalytic hydrogenation to form the same alkane. The heats of hydrogenation for each compound are shown in the table to the right. What can one conclude about the relative stabilities of Compound D 28.3 kcal/mole compounds C and D? A. C and D are of equal stability B. C is more stable than D C. D is more stable than C D. Impossible to determine from the information given Compound C 27.2 kcal/mole A Which structural formula represents a pair of geometric isomers? 9H3 A, CH3CH=cCHZCH3, B. CH30H=CISCHZCH3 c_ CH30HCH2CH=CH2 D. CH30H2CH2CH=CH2 CH3 CHZCHg ...
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