Exam3+key - Chemist 2311 Spring 2009 Exam 3 Chapters 5 and...

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Unformatted text preview: Chemist 2311 Spring. 2009 Exam 3- Chapters 5 and 6 Name ' KEY Part I. Indicate whether each of the following molecule pairs are [a] identical, [b] enantiomers, or (c) diasteriomers. (16 points) (a) (b) [d] CH3 Br K H H R Cl CH3 F Hficm H30 H OCH3 Cl Hlnhlcfic “.\\\\C| H/ \CZH5 F Hflcm H30 F H 49M CH3 HC/ 3 l/hhc/ H’ |K Br mink {80° CUthfl “CI 020‘“ 02H / 5 \H H30 H H CH CF 3 0 roiak l80 l A C-HIIIIIH I‘d-thta/ ; Part II. (a) Draw the 3-dimensional representation for each of the following. [16 points) 4 W4 [1] (2R,3S)—2-hromo—3-methy1pentane - 5r w. L4 .I'H 2:. 3 ‘ b . :- \/\( w a, ._ W H 8r ‘3’ 54 v w /1\./\ u w [2) [SJ-1,1—2-trimethylcyclopropane it [b] Write the complete IUPAC name for the following compounds. ’ j. H0 STww mm H \C—CH CH Cl . Clo“) 2 2 (35} 53* CIICMOTO Pendant H3CHZC F ch F ‘ H C H (3R) — 2,2,3— tri Fluorobtd‘ane. :2, grit/Vi Part III. Designate True (T) or False [F] for each of the following statements. [20 points) T '1'} Ti -‘l”n*n [a] A sample ofan optically active substance that consists ofa single enantiomer is said to have an enantiomeric excess of100%. [b] The (S) enantiomer of a chiral compound always rotates the plane of polarized light to the left. (c) The mesa form of a molecule can be either dextrorotatory or levorotatory. [d] trans—1,4-dimethylcyclohexane is chiral but the cis—isomer is not. (e) The difference in free energy between the reactants and the product is defined as the free energy ofreaction. If) The first step in the 8N1 reaction of tert—butyl chloride is the heterolytic cleavage of the carbon—chlorine bond forming the tert-butyl carbanio'n. (g) Carbon—hydrogen and carbon-carbon bonds located beta to a carbocationic center stabilize the cationic ‘species by hyperconjugative electron delocalization, [h] The Hammond-Leffler postulate states that the structure of a transition state resembles the stable species that is nearest it in free energy. [i] Nucleophilicities are related to rates ofreaction while basicities are related to equilibria. (j) Dimethylforrnamide and dimethylsulfoxide are polar protic solvents. Part IV. Complete each of the follbwing reactions. product when appropriate. [21 points] 3 M [3) Br H30 Nil—{Ni \ H , We \ _ H3C\\ l Acetone Water H C 3 H [b] H30 .C—O' K+ Br \‘ H3C\\\Y H3C H3O \ H \“‘C H30“ 1 “30 H30 H WC—OH H3C\\\/ H30 (0] (1) NaJr NHZ', liq. NH3 HgC"—C:__C—H —~——> A Show the stereochemistry of the H3C\ \ {H (2) \cC—Br CH3 02H5\\\Hl H (Egg (3) Pt, H2 (1 mole) qu‘U‘LbHrJ H2 H2 0 C C 50 C HSC/ \C/ \B + (L‘HgO‘Na+ mau- Hz CH3OH [0 H2 Br H2 0 c o H 0/ \c/ \CH 50 C 3 I 3 + CH30'Na” ———+ /CH2 CH30H H30 (3) Csz H \ / H Ethanol C~—~—-—C"“\\\ + Na+ CN' “M Br 3142 Part V. Answer each of the following questions. [30 points] [a] For each of the followin circle which reaction will occur faster. [1) 1—Brom0butane or 1—Iodobutane with sodium cyanide in dimethyl sulfoxide. [2] 1—Chloro-2-methylbutane o 1-chloropentane ith sodium iodide in acetone. [3r cyclohexyl chloride with sodium azide in aueous ethanol. [4] SoivOlysis of 1~bromo—2,2-dimethylpropane or tert—bu l bromide '11 ethanol. [5] Solvolysis of isobutyl bromide or sec-butyl bromid in'aqueous formic acid. (b) Give the mechanistic symbols [SN 1, 8N2, El, E2) that are most consistent with each of the following statements. (1] Methyl tosylate reacts with sodium methoxide in methanol only by this mechanism. 8 N 2 [2] Ethyl bromide, 1-bromopropane, 1-bromo‘outane, and 1-bromopentane react with sodium ethoxide in ethanol mainly by this mechanism. [3] The substitution product obtained by methanolysis of tertubutyl bromide reacts mainly by this mechanism. " (4) The elimination product obtained by acetolysis of tert—butyl bromide reacts mainly by this mechanism. a r 52 SNL El (c) Arrange the following carbocations in the order of increasing stability. CH3 CH3 l. _ 1113113 I H H H i. + l + ...
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Exam3+key - Chemist 2311 Spring 2009 Exam 3 Chapters 5 and...

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