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Spring 07 Exam 2 Key - CHEMISTRY 225 TEST#2 NAME Avast/um...

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Unformatted text preview: CHEMISTRY 225 TEST #2 MAY 25, 2007 NAME Avast/um. le7 GOOD LUCK! Useful atomic numbers: H = 1, C = 6, N z 7, O = 8, Si: 14, C1=17,Br : 35 TOTAL . (15 Points) CYCLIC COMPOUNDS. 3- (_ ._ 1. (15) 2. (13) 3. _ (19) 4. (14) s. (14) (75) I 8) Cyclopentene, structure below, is one of the simplest cycloalkenes. 0 (5) Write structural formulas for all derivatives of cyclopentene with a methyl group as the only substituent. D cyclopentene 0 (1) Identify the isomer that would exhibit the fewest lines in its 13'C NMR spectrum II (2) Write a structure for a weakly acidic isomer of cyclopentene. weakly acidic isomer (“.4 vairtl b. ( 1’ 2) A total synthesis of butylcycloheptylprodigiosin, the complex polycyclic compound to the right, was achieved recently by a chemist at Boehringer Ingleheim Pharmaceuticals {Org Lett. 2007, 9, 1879]. Suggest a reason why the name of this compound seems to conflict with its structure. 1-. "’97:.[0 .. (a. 9€L{L‘, -— ‘wibew '- \MéwL’VFK (.10 W nvuwA I Lam, ((1 vile—J NA- Buiyicycloheptylprodigiosin vlmJj ) OM17 5* aunt qr W?M—Lf'vr({ but]; 2 c. ( f 5) The properties of the unusual unsaturated hydrocarbOn to the right were studied recently [Tetrahedron Lett. 2007, 48, 3579]. o (2) Determine the number of signals (lines) in the 13C NMR spectrum of this compound. 47 'I X o (3) Account for the high degree of strain in this compound on the grounds of structure and b nd'n .HINT: ‘onstruct amodel. --\_ ' O ] g L . fl“: é—L‘.‘ ;'L x- LE 'x—‘fl : x...- \} --. flux. _: 14; mat“ Teuvrt ie- TL: VL-Hze rcm(W.L_--.er-=! »\_j. m niiwlfvw—aKE may? sumo“ Lt will Low-.43 Wt...» 2 a: [LWI “Us... mete: aw: if? c tum.) Osaka e FEM} as that wan/fl...) 71‘s., is.“ 711,411 retry-«HI Valetea. View; «In: excrete eaL/aes. 2. (13 Points) ROTATIONAL ANALYSIS. -— CM 5 a M. “14,: fly! t _ w c L ’ J 3. (f i’ 9 ) Consider bond rotation in 3,4—dimethylhexane. V K‘ o (4) Provide Newman projections for the three staggered conformations of 3,4-dimethylhexane looking down the C(3)—C(4) covalent bond. 0 (3) Circle the most stable rotational isomer and briefly defend your choice. I (2) Write a structure for an isomer of 3,4-dimethylhexane with three structurally unique (nonequivalent) carbon atoms. CaH18 structural isomer 3 b. ( l 4) One of the few organic reactions that alkanes undergo is photochemical halogenation, a reaction in which a halogen replaces a hydrogen upon irradiation with ultraviolet light (symbolized as hv). Complete the photochemical chlorination reaction below with structures for all monochlorination products (C6H13Cl). Ignore the side product, HCI. U 9H3 rb’ CH30H{|3HCH3 + CI2 41+ CA; Ul CA4 CM, CA 1 CH3 0”} 3. (19 Points) ORGANIC REACTIONS. a. ( l 6) Complete the following organic reactions with structures of the products. b. ( f 6) Consider the acid-base reaction below: 0 O l I! E) CH3CC HgCC H3 + CH3C H20 CHSCC HCC H3 + CH30 HQOH 9 i, é be 0e t (4) For the reaction in the lefi to right direction identify: the acid (A) the conjugate acid (CA) the base (B) the conjugate base (CB) 0 (2) The two species on the right are favored at equilibrium. Identify the stronger acid in this reaction. Justify your choice. ' ii “‘9 film,“ {V at; Aci ("i /La¢e V'KNG [*vov _ Tint wia iI/(v ac‘ui. é‘wtfi TL! {7 uh)“ L"'“W 2" wit?) Tim v'ijLiJ ‘j‘Lt J‘icrc‘ioug wug‘i‘ Le 11‘! Q'lv’nutj{./ (Leif! 4 c. ( t 4) Consider the addition of HBr to an alkyne. As shown below the reaction proceeds in a stepwise fashion by way of an aikenyi halide. The alkenyl halide then reacts with a second molecule of I—IBr(g) to give the final product. HBr H39 zBr H+ HIV B ‘ _ _ r CH30:CCH3 "—"" R’C—q ——"’ w ____ C —-~—I‘- CH3CH2CBTQCH3 H CH3 1 (’19 email!” ha'ide catidiiic intermediate 0 (2) Determine the geometry at the double bond of the alkenyl halide (circle one). cis- E— trans- Q o (2) Write a structure for the cationic intermediate of the second step. d. ( t3) An article in this week’s issue of Chemical & Engineering News describes a new method for the synthesis of secondary amines involving addition to a terminal alkene. The general reaction format is shown below. tantalum catal at 0\ ,CH3 + HCH=CH2 #————y——-- 0 H H H CH3 Use the functional approach to deduce the structure of the unsaturated reactant in the example below. N/ 3 / H H CH3 4. (14 Points) NOMENCLATURE AND UNSATURATED COMPOUNDS 3. '6 t 6) Consider the unsaturated compound A (a diyne) below which was used recently as a reactant in a study of certain ring-forming reactions [Org Lett. 2001Ir , 9, 1907]: /\/\/\ H2! catalyfi as //' ~———»~ compound A 0 (3) Assign the IUPAC name to compound A. HINT: The name of the C11 alkane is undecane. a}, 8 - LkmAé C(lcxlvv‘i :- {3) Complete the reaction of compound A with a structure for the product. You may assume that the hydrogen is in excess. 5 b. ( f 3, BONUS QUESTION!) Complete ONE of the following questions. If you answer both you will get credit for the one best answer. l —Write a jagged line formula for 2,9-dirnethyldeca- l ,9—diene- 4,6—d1yne [Org Lett. 2007, 9, 1851]. “2:; "" :.::“—\a-;..r i —Provide the IUPAC name for the unsaturated tetraene below. I \ \ CH3 1% CH3 E 1” (LE CC" Fr 2! 4f "e— LE» ?’ me: C. ( r 5) Consider the unsaturated compound below, a marine natural product recently studied by chemists at the University of Califomia, San Diego [Org Lett, 2007, 9, 1975]. ‘ Br \‘ - r /\ 1 “Le Ha I (3) Directly on the structure locate all double bonds with the (E)—configuration. o (2) Write in all allylic hydrogens and label them as Ha. d. { K 3) The compound below has been utilized as a reactant by Japanese chemists in a synthetic route to elaiolide, a potent antibiotic against Gram-positive bacteria [Tetrahedron Lett. 2007, 48, 3163]. Directly on the structural formula locate all bonds about which there is free rotation. To help you get started, one such bond has already been located. 0 ..- ll CH3&'CH2}03:C CH:CH&CH:CH3® 5 . 5. (14 Points) MULTIPLE CHOICE. Write the letter of the most correct response in the space provided to the left of the question. . . H g 1 Vinylacetylene is an industrial chemical used in the synthesis of H_CEC#CI neoprene. The structure of vinylacetylene is shown to the right. Which of _ \b_H the following is an accurate description of the structure of vinylacetylene? V'Wlacewlene H” A. One acetylenic hydrogen, one propargylic hydrogen, two vinylic hydrogens. B. One acetylenic hydrogen, one allylic hydrogen, two vinylic hydrogens. C. One acetylenic hydrogen, three vinylic hydrogens. D. One propargylic hydrogen, three vinylic hydrogens. 6 D Which of the compounds below violates Bredt's rule? p4 Estimate the barrier to rotation about the C(3)~C(4) bond of n-hexane. A. 5 kcalr‘mole B. 15 kcalfmole C. 65 kcalx’mole D. 90 kcalfmole @ Which of the following terms best describes an alkynyl (acetylide) anion? A. Weak base B. Conjugate base of a very weak acid. C. Conjugate base of a strong acid D. Weak acid ID Determine the dihedral angle between the two methyl groups in the anti conformation of butane? A. 0° B. 60° C. 120° D. 180° D Which of the following compounds is capable of geometric isomerism? \ CH3 9H3 A. |' B. CHscHzoECCHecHE C. CH30H20H=C: D_ CHGCHQC=CHCHZCH3 CH3 A What is the common name of the branched alkyl group to the right? C(CH ) — 3 3 i A. Ierl—Butyl B. Neobutyl C. Isobutyl D. Trimethylmethyl w ...
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