322as08_final_key

322as08_final_key - A Chemistry 322aL Name I ; t Basic...

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Unformatted text preview: A Chemistry 322aL Name I ; t Basic Organic Chemistry Last / First May 7, 2008 FINAL EXAMINATION Please answer the following questions in the space provided. Please organize your thoughts and attempt to make your answer as legible as possible. If we cannot read your answer, it cannot be given credit. Also, remember that C-C—C-C without hydrogens and “stick” structural representations will be given N0 credit (except for rings only). 1 (26) n MM“. (2.6 III (60) IV (20) v (20) v1 (21) TOTAL (201 ) Chemistry 322aL Final Examination page 2 May 7, 2008 I. (26 pts) Provide a name for the following structure, and a structure for the following name. Use Z, E, R, and/or S as appropriate. (a) Clia ,CH3 < C':H CliHa CH CH2 CH O \r‘ OH (b) HI". I..|IIC)*-' G F CHZC H3 (d) Neopentyl alcohol (e) DMF 0 [CH6 “C N/CH’b Cuycfcukon IJ’ w”; 0143 (l m ":3 I (f) Benzyl methyl ether (g) THF CH3‘ 0“ Ci‘iz Chemistry 322aL Final Examination page 3 May 7,2110%”. > 11. (54 pts)K Q 7 " a) Which is the least stable conformation of cyclohexane? A) Chair B) Twist Boat @ One-half chair Staggered b) Which of the following is NOT true of enantiomers? They have the same: A) boiling point. melting point. pecific rotation. density. E) chemical reactivity toward achiral reagents. c) The device that is used for measuring the effect of optically active compounds on plane- polarized light is called a . . pom r \ m Give. l‘ (1) Which statement is n_ot true for a mesa compound? A) The specific rotation is 0". B) There are one or more planes of symmetry. C) A single molecule is identical to its mirror image. More than one stereogenic center must be present. ® The stereochemical labels, (R) and (S), must be identical for each stereogenic center. e) Which of the following is true of any (S)—enantiomer‘? A) It rotates plane-polarized light to the right. B) It rotates plane-polarized light to the left. ,- .\ It is a racemic form. (Q; It is the mirror image of the corresponding (R)-cnantiomer. -.) It has the highest priority group on the left. Chemistry 322aL Final Examination page 4 May 7, 2008 t) Elimination reactions are favored over nucleophilic substitution reactions: A) at high temperatures. B) when tert-butoxide ion is used. C) when 3° alkyl halides are used as substrates. D) when nucleophiles are used which are strong bases and the substrate is a 2° alkyl halide. @in all of these cases. g) Which is a true statement concerning the transition state of the rate-determining step of 1 reaction? Structurally, it closely resembles the carbocation intermediate. Both covalent bond-breaking and bond-making are occurring. C) Formation of the transition state is an exothermic reaction. D) Necessarily, the transition state has zero charge overall. E) More than one of the above h) The Hammond postulate when applied to nucleophilic substitutions and elimination reactions states that: A) a negatively-charged nucleophile is stronger than its conjugate acid. B) polar aprotic solvents strongly accelerate the rate of 8N2 processes. ‘ bimolecular nucleophilic substitutions are 2"" order kinetically. the transition state for an endergonic reaction step (one accompanied by an ’ increase in free energy) structurally resembles the product of that step. E) elimination reactions will always compete with nucleophilic substitution reactions. i) An equimolar mixture of two enantiomers is called a C CW (it . 0v racewc wind LL j) Zaitsev's rule states that: A) In electrophilic addition of an unsymmetrical reagent to an unsymmetrical alkene, the more positive portion of the reagent will become attached to the carbon of the double bond bearing the greater number of hydrogen atoms. B) An equatorial substituent in cyclohexane results in a more stable conformation than if that substituent were axial. C) E2 reactions occur only if the [3-hydrogen and leaving group can assume an anti- eriplanar arrangement. 'hen a reaction forms an alkene. and several possibilities exist. the more (or most) stable isomer is the one which predominates. E) The order of reactivity of alcohols in dehydration reactions is 3° .2 3" 7' 1°. Chemistry 322aL Final Examination page 5 May 7, 2008 k) The rule that correctly predicts the regiochemistry of most ionic additions of an unsymmetrical electrophilic reagent to an un mmetrical alkene is called ' '5 WWW 0\lv\\\‘{0\l . 1) When a reaction that could potentially yield two or more constitutional isomers instead produces only one as the major product, the reaction is said to be PegIOSQQO§ig . m) in general, when the addition of an unsymmetrical electrophilic reagent to an unsymmetrical alkene forms the product predicted by the rule mentioned in 90 above, that occurs because: A) the product is statistically favored. steric hindrance favors its formation. ©it is formed via the more/most stable carbocation. it is the more/most stable product. E) All of the above are reasons. n) When a particular stereoisomer reacts in such a way that it gives a particular stereoisomer as a product, even if more than one stereoisomer is theoretically possible, the reaction is said to be Stereospeci Em. . o) A reaction in which the reactant is not necessarily chiral but still produces primarily one stereoisomeric form of the product is referred to as a : 2+®m0 Sale th‘Ue/ _ reaction. Chemistry 322aL Final Examination page 6 May 7, 2008 p) In the structure shown, Ha and H, are classified as: HO H e a Rb A) homotopic protons. B) vicinal protons. ’ nantiotopic protons. (a o iastereotopic protons. ’ isomeric protons. q) Which of the following could be used to synthesize 1-bromopentane? ‘ CH3CH2CH2CH=CH2 + HBr ——-) H3CH2CH2CH2CH20H + PBr3 ———> CH3CH2CH2CH2CH20H + NaBr ————) D) CH3CH2CH2CH2CH20H + Brz —————+ E) CH3CH2CH2CH=CH2 + Brz ——> r) Which of the following reactions would have the smallest energy of activation? A)>k/k/+Br._> *JV+HBr B) >Ivk/ + Br' M + HBr m + Br. -—> M + HBr D)fl\/l\/+Br.——> M+HBr E) >|\/k/ + Br. + HBr 5) Which reaction would you expect to have the largest energy of activation? AH" (kJ mol") A) CH3- + CH3. ———> CH3CH3 -378 CH3- + Br- —————> CH3BI‘ -l30 CH4 + I- ———> CH3- + H1 *142 CH4 + Br- ——> CH3' + HBr +104 E) + ——_—) ‘1‘ “‘8 Chemistry 322aL Final Examination page 7 May 7, 2008 t) An example of a reaction having an Eng. close to 0 would be: A) Br- + Br—Br ——-) Br—Br + Br- F- + CH4 —-——> H—F + CH3- ©CH3' + C1- ——> CH3C1 More than one of these E) None of these u) If chlorocyclopentane were chlorinated to form all possible dichloro compounds and the product mixture subjected to precise fractional distillation, how many fractions would be obtained (ideally)? A) 3 4 (§ 7 E)9 v) A chain reaction is one that: A) produces molecules with long chains of atoms. B) involves two steps of equal activation energy. :x.\ one that can be initiated by light. 59) nvolves a series of steps, each of which generates a reactive intermediate that brings / about the next step. E) involves free radicals that have an unusual stability and thereby cause a large quantum yield. w) An alternate mechanism for the chlorination of methane is: AH° (kJ mol") C12 —-——> 2Cl- Cl—Cl 243 C1- + CH4 ———> CH3C1 + H- CH3—H 440 H' + C1: ————-) HCl + Cl- CH3~C1 352 H—Cl 432 This mechanism is unlikely because: A) The overall AH° is highly endothermic. B) The probability factor is low. One of the chain propagating steps is non-productive. ne of the chain propagating steps has a very high Em. One of the chain propagating steps 15 highly exothermic. Chemistry 322aL Final Examination page 8 May 7, 2008 x) Free radicals can be produced by: - A) use of high temperatures. B) irradiation with light. C) reaction of a molecule with another free radical. both A) and B). all of A), B) and C). y) Macromolecules made up of many repeating subunits are called W e l‘ S Q. 2) The reaction between l-pentanol and HBr to yield l-bromopentaiyis probably: .‘ an SNl-type reaction involving the protonated alcohol as the substrate. \a : SNZ-type reaction involving the protonated alcohol as the substrate. ’ an El-type reaction involving the protonated alcohol as the substrate. D) an EZ—type reaction involving the protonated alcohol as the substrate. E) an epoxidation reaction. aa) What is the relationship between alcohols I and 11? H CH3 CH3 H OH H H OH I 11 They are: A) different conformations of the same compound. constitutional isomers. nantiomers. diastereomers. E) identical. Chemistry 3222L Final Examination page 9 May 7, 2008 III. (60 pts) Provide structures for the organic product(s)f0rmed in significant amount in the following reactions, or show the reagents required to carry out the indicated transformation. Be sure to show regiochemistry and/or stereochemistry when appropriate, including R, S, E, and/or Z designations if warranted. Please remember that C-C-C-C without hydrogens and “stick” structural representations will :e)given no credit (except for rings). H no :Q I _ l a CH3 1) Tosyl chloride In ... / m S Hume/OH pyridine 3‘ l l0 A l 2) KOH f + C H H We pure. 6 13 DMSO Product has a strong, C6 lg n a enan’tlomer broad IR band at 3400 cm“1 ' MM*\\lflf—:ir Dial W (b) Cu ‘ ggr CH3 1) Hg(OCOCF3)2 / b ,. HOCH3 ___. no eleveoc om l\/‘ l 2) NaBH4, NaOH 004 b - 0R (c) O conc.HBr er (g Cl/Afinr excess, hot Cit/H fill-l2 r L CH (d) CH3 /\‘/3fi \ HO / W \ l Br (c) \L‘ »\ CH2 /CH2 » Brz _,_ / CHLCH CHJCH {fir \CHL \CHg CCI4eoivent U A 3 i—BuOOt—Bu A Chemistry 322aL Final Examination page 10 May 7, 2008 1) THF BD. Q”6 mi M16: 5% w ' (J (0 in THF solient /\[vu D \v Q/CHa ¥—~/ (racem'x a) 2) H202. OHH "a. 0 H (* recall, D = deuterium, an isotope of hydrogen) LOYOHS S+eréo Ulr‘ém "‘ 2 710+ HQCQCEd r (g) Cpg . 0/ CF13 B HZO/THF solvent / who“ i _ r2 ———>(dark) (5P (m come) Lora n5 siereoim —-l " main --l (h) CH3 CH3 ' CH4; CH3’C"'-(\/[{'CH3 NaOCH3 CH3L"~/\L0H siéreocizcm ' O “'30” K/L’MC”; maid i (i) O m + J\OOH CHaoH A C O J? M O-ié g ‘ fl Ylgwacm «x (j) /\¢CH2 CC|4 soivent + HBr »——_» ,1 §‘—/ (9) t-BuOOt-Bu [— A Chemistry 3223L Final Examination page 11 May 7, 2008 00 H3 0 CH2CH20H CH _C/CH3 H2304 G\/'\/, CHZCHfO— "- 04; KO/ + 2— \CH3 (catalytic) CH3 1) BH -THF GCH=CH2 ina'rHF OIL—CH 2QH10H 2) H202, NaOH r I Bra (dark) (5" (Pa CGMM'C J CCI4, 0 0C (5 P Chemistry 322aL Final Examination page 12 May 7, 2008 \J‘ 3 (o (D C F33; 0K (13) _——_—> 2) NaHSO3, H20 (q) 9 1>0so4. pyridine /\/..0H S—iereo i ° C) (r) CH3 1) 03 cold H l ' /C’\C CH CH 6"; H 0/ 2) Zn, H20 CH3 HKCH‘ ‘ 1 (S) HBr 6“ CHBCWCWCECH (anhydrous, excess) CH1 C‘H‘z d_ CCI4, dark, cool ream M6)" heuscav CH9 / B / CH3 u . CHCI3,KOt-Bu ’ (>< racemc 0/ hexane Cl ( Chemistry 322aL Final Examination page 13 May 7, 2008 IV, (20 pts) Provide reasonable syntheses (i. e., minimum number of steps. good yields, good regiospeciflcity, stereoselectivity, stereospecificity, etc.) for the molecules specified below from the t0 indicated starting materials and any other needed solvents or reagents. Be as specific as you can M regarding reagents and conditions. Show the product formed from each important step of your " syntheses. CH CH 2 3 (a) HO\ AH (Ma CH1 0. H H CH3CH2CECH ------------------------------ --» $ + Q \ +9.”, N ,c ~ “a 2 (Note that making the mono-ether from the diol H"? \ O \ $ [I6 would give an unacceptably low yield.) CHSC H2 OCH2CH3 ® “H3 :‘6 Ha I” (a) ndl’ “w‘mg /0 Ct CHBCH) cad-3 Na 1 C “\C \ #0 pa” X EL— If 211‘ Et i Quacuzear‘ \x J ' ’ 0 II ‘3 ~04 CH ‘4‘ H R400” Cl—lJJ—lz C C 2&3 /C_____ (R < If H} LII/l ar 5 0433C”) CH1 CH 3 A an 3 or Ni 3,. —————————————————————————————— m a —\ §( a cum; 43"? Ma Cue“ fie) Ch? 0W8 m THF (5/ ;\\OWL CH3 ~—- .\ eanF / l . NOH /: ‘m TM: ’ 2) Hsz Ef ’"* x Chemistry 322aL Final Examination page 14 May 7, 2008 - V. (20 pts) Organic thiols (RSH and AISH) undergo additions to alkenes initiated by light or peroxides and heat, as shown below. Some randomly selected specific homolytic bond dissociation enthalpies are tabulated at the right. Specific Bond Dissociation C H3 t.Bu_ O- O- t.Bu C H3 Enthalpies (kJ/mole) 0/ + H-S-Ph -————-> ____——“_ A H - H 436 (Ph = phenyl. CeHs) S-Ph 3,43, 193 0 Show the initiation step, the two propagation steps, and org H_Br 366 example of a termination step that you would predict for the mechanism of this reaction. (C H3)3C - H 400 o In the box at the right, show the enthalpy change for each (C H3)2CH-SPh 307 individual step. Show your reasoning in the space below each reaction. Phs _ H 350 0 Calculate the enthalpy of the overall reaction as shown above. R3Sn_ H 264 2 Initiation: {Bu0_0_{Bu A; 2 as“) Rash—Br 552 C=CnBond 270 2. {Bu0'+ 14895 ——=7 {Ewan + 933. Progagation: Reaction 1 '2— 2 gs. + M; —_> m / + 270 -— 3m 3}” Reaction 2 '2. (1 z + “$523 a q;: to $93 + 3'50 — H00 Termination S“ or 0mg 0% «*1? C. \/ o '43 ——a QC” ' ‘ A / + \ $53 5 X +3 9 x3 Real/mole at atom :7 ( 4;? Chemistry 322aL Final Examination May 7, 2008 page 15 (b) The above thiol addition of thiophenol also proceeds with 1,5-cyclooctadiene as shown below. When a large excess of the diene is used, but the thiophenol concentration, [HSPh], is also fairly high, monoaddition product A predominates. When the concentration [HSPh] is low, bicyclic product B is the main product. 0 Explain the effect of [HSPh] on the A/ B ratio. t-Bu-o—o—t-Bu SPh SPh + H—S-Ph —> + A A B was %¢ \ Low [Hsgfl /\ 3}” % \wég (MSW)! can Com (Wale— HS¢ $¢ $0. 5/25 Chemistry 322aL Final Examination page 16 May 7, 2008 VI. (21 pts) (a) Write the letter of each of the three infrared spectra below in the space under the single compound of which it is the spectrum. (Fill in ONLY three blanks) (‘3 CH3 4000 3000 3200 2000 2400 2000 1000 1000 1400 1200 1000 000 000 499 H i Q Q / C\ Frequency (cm-U 1? CH ff, ' \ \\ Frequency (cm") ,2" _C___N } 4000 3600 3200 2000 2400 2000 1000 1600 1400 1200 1000 000 600 490 3 2 2 — g / again-n::Iaulllnaqlaaaamnl “harm, fillllllhlfillllll ...l II 3 C , ..:: may 1 _,r till Illfl \ i ' ""(fH'g'CchHz-CEC-CHzcm I." an: Il‘ mama“: Frequency (cm") 4000 3000 3200 2000 2400 2000 1000 1600 1400 1200 1000 000 600 499 ‘\ :=,==:==:=.-=.-:::. flap-«- v ~> - v—-- w . WM CH3(CH2) 4CI-I2- OH ’3, I! ‘y‘ \ \\ “‘\ ‘~~-~.~r,,.;»::;,:7§_".fi - ‘O\ z" // llllllllIII II:- CH3(CH2)4CH2- C\ ‘ ===I:IIIII III. 3 e iii-NIF“ -" ‘ "““ ' - unuiiififihflflfilflfllhfl "" C Efilflflllllfl .,_ 1 ~ "IHIE I I I Chemistry 322aL Final Examination page 17 May 7, 2008 (b) The 1H NMR spectrum below is of the compound C9H|00. Give its "unsaturation number," U, consistent with this molecular formula, and provide a structure fully consistent with the spectrum. Be sure to show your assignments by labeling each peak in the spectrum and placing the corresponding label next to the appropriate hydrogens in your structure — the correct structure alone is not sufficient for full credit. The integral of each set of peaks is given on the spectrum. Chemistry 322aL Final Examination page 18 May 7, 2008 (c) Follow the same instructions to provide a molecular structure corresponding to the "’C NMR spectrum of C5Hl 1C1 shown below. The assignments as to the number of hydrogens could come from either DEPT or off-resonance decoupled spectra. \i‘ (a (a @043— , —CHJ~ CH3 CH5 (4) 2 S—Hual‘uflx 2 Ann b'l‘dl’d” ...
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This note was uploaded on 07/13/2008 for the course CHEM 322AL taught by Professor Jung during the Spring '07 term at USC.

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322as08_final_key - A Chemistry 322aL Name I ; t Basic...

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