topic6practiceprobans - gb i Li Chemistry 2311 Topic 6-...

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Unformatted text preview: gb i Li Chemistry 2311 Topic 6- Practice Problems 1. Which compound undergoes substitution by the SN] mechanism at the fastest rate? (1) Mm <2) /l\(\ Br Br (3) 2. Which compoun ergoes substitution by the 8N2 mechanism at the fastest rate? Wcsi/Ji’z‘L/(f (,JLD oil“) A 3. What is the effect of doubling the concentration of sodium bromide on the following 8N2 reaction? H3c\C/CI + Nal ___’H3C\ /l + Nam 2,1; H2 H2 “$1 b I - . e o the reaction double (d) There is no e ect. 4. Which of the following is a polar aprotic solvent? (at) methanol (b) acetic acid (0) hexane d) N,N—dimethylformamide 5. Which of the fol] _' n 1 ions has the most nucleophilic reactivity in methanol” (3) fluoride ion c) potassium ion ((1) tetrafluoroborate ion, BF4” 6. Which of the following bonds has the lo -- =: d dissociation enthalpy? a. C-H b. C-F c. C-Br w 7. Which of the following statements is not true regarding the halogenation of alkanes upon treatment with halogen and light? a. bromination is more selective for 3° positions than chlorination ' b. the reaction proceeds via a radical intermediate 0. ' ' ' reaction . this is a useful process for the formation of fluorides, chlorides, bromides and iodides (a) The rate constant, k, doubles. (c) The products of reaction Change. \ (EA/c1] 9w} 8. What is the major organic product obtained from the following reaction? 9. What is the characteristic of a radical chain propagation step? a. radicals are formed . e formed ive a new radical and a new molecule 0 ralcals combine to give a molecule 10. What type of reactive intermediate is formed upon irradiation of a solution of toluene (Ph-CHa) and bromine? a. benzylic carbocation b. benzylic carbanion O ‘ 0 . . V I romonium ion 11. Which of the following alkanes does not undergo monobromination to form a single bromoalkane as the major product? QxW 1 a.1 b.2 c.3 ® 12. What is the correct order of stability of the following radicals (more stable > less 1 2 13.1>2>3 b.1>3>2 c.3>1>2 Q 14. What is the major organic product obtained from the following reaction? 15. In each ofthe following cir ‘ A..- ' - - action will occur faster. (1) 1-Bromobutane or 1-Iodobutan ith sodium cyanide in dimethyl sulfoxide. (2) 1-Chl -2—methylbutane r 1—chloropentane ith sodium iodide in acetone. (3 r cyclohexyl chloride with sodium zide in aqueous ethanol. (4) ‘ -bromo-2,Z-dimethylpropane or ebutyl bromi in ethanol. (5) Solvolysis ofisobutyl bromide r C—butyl bro 1n aqueous formic acid. 16. Give the mechanistic symbols (SNl, 8N2) that are most consistent with each of the following statements. (1) Methyl halides react with sodium ethoxide in ethanol only by this mechanism. SN L (2) Unhindered primary halides react with sodium ethoxide in ethanol mainly by this mechanism. SN L (3) The substitution product obtained by solvolysis of tert-butyl bromide reacts mainly by this mechanism. 9“) \ Section II. Indicate True (T) or False (F) for each of the following statements. ( (a) Increasing the concentration ofthe nucleophilic species in an 8N1 reaction increases the rate of reaction. 1'“ (b) The SNZ reaction occurs by a back-side attach of the nucleophile and the carbon bearing the leaving group. IC (c) The difference in free energy between the reactants and the transition state is defined as the free energy ofreaction. F (d) The smaller the free energy of activation the slower the reaction. /J'— (e) The overall rate in a multi-step reaction is controlled primarily by the slowest step in the reaction sequence. 4 (f) The first step in the 5N1 reaction of tert-butyl chloride is the hemolytic cleavage ofthe carbon—chlorine bond. { (g) Carbocations have a trigonal planar geometry. (h) Carbon-hydrogen and carbon-carbon bonds located beta to a carbocationic center stabilize the cationic species by hyperconjugative electron delocalization. T (i) The Hammond-Leffler postulate states that the structure of a transition state resembles the stable species that is nearest it in free energy. 1/ (j) Nucleophilicities are related to rates of reaction while basicities are related to equilibria. F (k) Dimethylsulfoxide is a protic solvent. Section 111. Complete each of the following reactions. Write the structure of the principal organic product to be expected from the reaction of l— bromopropane with each of the following: N 2,, p 1 S d' ' d'd ' t [) 01um101e1naceone ‘Fl’nm /\ /\//l— [2) Sodium ethoxide in ethanol NOE} [3) Sodium cyanide in dimethyl sulfoxide /\/0" Identify the product in each of the following reactions: H2 H2 Cl C C Nal (1 mole) (1) \c/ \CH/ \CH3————> C5H10|C| H2 I Acetone CI P W C1 B 82 H2 (2) r NaS C \E/ \B + \S/ \SNa—> C4HBSZ 2 2 Cu) P Q N _ 4 ‘ BrCHZCOCHZCHg \/\\ 0/\ - 0 CH gm 0 no (1 ., ’ I a acetlc amd \ NaCN “ ————> CH3CHQOCH2CHzBr ethanol—water /\O/\/ CA) __ CM mo, H NC O—CHQCI “A E? (H) OH NaNg C1CH2COC(CH3>3 W (Vi/Pg 0 CH3 Na! 0 L ><CH3 acetone 3: OX TsOCH2 0 / \ + CH CH B "'9 < QCHZSNa 3 2 r /(D\/S/\ OCH3 CH3O CHQCHQCHzCflgoH 1. TSCI, pyridine ——————-> 2. Lil, acetone CH3O / O O 013 5/ K / ) \ f 7:. o Bu I ~ ‘ 6 /j\/\/ V r O _ j ‘ / o Section III. Devise a stepwise mechanism for the following reaction. CHacHgoe 0 CH3 VI 0 HSCVO\/L\CHS + Ole “ “‘9 $906 “9 /—<<O C /0 do GO gulch “5% Le.) d5 Q 6/5 / n 4: )W/MDA C/ LC! *6 Q Ci' \L ...
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This note was uploaded on 10/24/2010 for the course CHEM 2311 taught by Professor Tyson during the Spring '07 term at Georgia Institute of Technology.

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topic6practiceprobans - gb i Li Chemistry 2311 Topic 6-...

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