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322af02_final_blank - CHEMISTRY 322aL/325aL FINAL EXAM...

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Unformatted text preview: CHEMISTRY 322aL/325aL FINAL EXAM DECEMBER 12, 2002 Please _________________ Print Last Name _________________ First Name SSN ______________ TA's Name____________ Lab Day & Time_________ (1) (45) _____ (2) (20) _____ (3) (20) _____ (4) (15) _____ (5) (30) _____ (6) (15) _____ (7) (20) _____ (8) (10) ______ (9) (25) ______ (200) Grader ______ ______ ______ ______ ______ ______ ______ ______ ______ first letter of last name I will observe all the rules of Academic Integrity while taking this exam. _______________________________ Chemistry 322aL/325aL Final Exam -2- Name_____________ (1) (45) Complete the chemical reactions below by providing the organic product or products (as requested) within each box. You do not need to show byproducts of the reactions or any mechanisms. Show or describe stereochemical details in the products wherever they are important. "Workup' means adding water and bringing the solution to neutral pH. Br (A) CH3 H C8H13N H + Na+ -C N CH SOCH (DMSO) 3 3 (B) CH3 CH3 H2 Pd (C) CH3 OH CH3 C CHCH3 CH3 conc. H2 SO4 heat C6H12 Product decolorizes cold KMnO 4. Product shows single resonance in 1H NMR. (D) Br CH3 CHCHCH3 + NaOEt ethanol CH3 Product decolorizes Br2/CCl 4. Show major product only. (E) CH3 + HBr no peroxides C6H11Br Chemistry 322aL/325aL Final Exam (1) Contd. -3- Name_____________ (i) hot KMnO4, HO /H2O CH3 CH2 CH2 H (F) C=C (ii) workup, H3O+ H CH2 CH2 CH3 - C4H8O2 H2 Pd/C (poisoned catalyst) (G) C 6H5C CCH2 C6 H5 Product decolorizes Br2/CCl 4 (H) (CH3 )2C O CH2 NaOCH 3 CH3OH C5H12O2 (I) CH3 (i) Hg(OAc)2/THF, H 2O (ii) NaBH4, NaOH ir: strong bands 3200-3500 cm-1 OH (J) + SOCl2 Product gives a ppt with alcoholic AgNO3 Chemistry 322aL/325aL Final Exam (1) Contd. -4- Name_____________ (K) CH3 CHCH2CH=CH 2 CH3 THF.BH3 THF C6H15B CH3 (L) CH3 CHCH2CH 2OH (i) NaH (ii) CH3CH 2CH2CH 2Br C9H20O (M) CH3 CH2 CH2 CH3 CH2 OH C CH3 conc. HCl 25oC single enantiomer Product is insoluble in cold conc. H2SO4 and give a ppt with alcoholic AgNO3 (N) CH3 CH2 H C=C CH3 H + CO3H CO22 C5H10O (i) H2SO 4 (ii) CH2 =C(CH3 )2 C8H18O Mg2+ ethanol (O) CH3 CH2 CH2 CH2 OH Chemistry 322aL/325aL Final Exam (2) (20) Answer the questions below. -5- Name_____________ (A) (10) All valence-level electrons are shown in the structures below. Provide any missing formal charges in these structures. Place the charges immediately next to the atom on which they reside. Not all of the structures have missing formal charges. :O H CH3 CCH3 CH3 CH2 CHCH3 . H H-B-H H = : H H H C=N H CH3 CH2 CCH3 CH3 CH3 CH2 N: CH3 (B) (10) Indicate on the line below each structure whether the structure is chiral or achiral. In each structure, identify all stereocenters with an asterisk (*). A stereocenter is defined according to the definition in lecture and in our text. CH3 CH2 CHCH2Cl CH3 CH3 CH=CClCOOH C 6H5CH 2CH(CH3 )2 O CH OH = H OH H H OH CH3 Chemistry 322aL/325aL Final Exam (3) (20) Answer the questions below. -6- Name_____________ (A) (10) Identify the pairs of structures below as constitutional isomers, enantiomers, diastereomers, or same compound. Be careful to select the most precise defining term. CH3 Cl CH3 CH2 CHCH2CH 3 Cl CH3 CH2 CH2 CHCH3 H CH3 H H CH3 CH3 H CH2 C 6H5 H C CH3 NH2 H2N CH2 C 6H5 C CH3 H H Br CH3 Br H CH2 CH3 Br H CH3 H Br CH2 CH3 CH3 CH3 C=C Cl H CH3 CH3 C=C H Cl (B) (10) Provide detailed structures of the following compounds in the boxes below. Your structures must show the stereochemical features indicated in the name. (Z)-1-chloro-3-methyl-2-pentene cis-3-methylcyclohexanol (most stable conformation) Chemistry 322aL/325aL Final Exam -7- Name_____________ (4) (15) The 1H NMR spectra of three isomeric ethers of formula C4H10O are shown below. Assign each spectrum to the proper ether structure (I, II or III) by drawing the correct structure inside the box next to the spectrum. Assign the groups of magnetically nonequivalent H in each structure to the resonances in the spectra with arrows. If two groups of magnetically nonequivalent H are not resolved in a spectrum, draw arrows to the general location of their chemical shifts. Isomers of C4H10O CH3 CH2 OCH2CH 3 I CH3 CH2 CH2 OCH3 II CH3 OCH(CH3 )2 III Chemistry 322aL/325aL Final Exam -8- Name_____________ (5) (30) Circle the correct answer for each statement or question below. (A) The correct molecular formula for the structure below is (circle answer below) C 6H6O C 6H10O C6 H9O C6H12O (B) The constitutional isomer of C5H10O with the highest boiling point is CH3 CH2 OCH2CH=CH 2 O CH3 CHCCH3 CH3 O CH2 =CHCH2 CH2 CH2 OH CH3 CH2 CCH2CH 3 (C) The configurations of the stereocenters in the two compounds below are CH3 (D) The order of acid strength (strongest to weakest) of the following compounds is NH3 I (circle answer) (E) The strongest acid among the following carboxylic acids is (circle answer below) CH3 CHClCOOH (circle answer below) (F) A cyclohexane conformation that has no torsional or steric strain is O = = H C OH Cl H CH2 CH3 CH=CH2 II C (circle answer) I (R) II (R) I (S) II (S) I (R) II (S) I (S) (II (R) CH2 CH3 I CH3 CH2 C II CH CH3 CH2 CH2 CH2 OH III IV>II>III>I CH3 CH2 CH2 COOH IV IV>I>III>II IV>III>I>II IV>III>II>I CH3 CCl 2COOH CH3 CH2 COOH ClCH2 CH2 COOH Chemistry 322aL/325aL Final Exam (5) Contd. -9- Name_____________ (G) Which statement is not true about nucleophilic substitution (Nu) of an alkyl halide (RX) by the SN2 mechanism? -The general form of the rate expression is rate = k[RX]{Nu]. -The rate of the reaction slows down as alkyl groups replace H around the reacting center. -The rate of the reaction increases when the solvent is changed from polar protic to polar aprotic. -The reactivity of RX depends on X in the order F>Cl>Br>I. (H) The proton decoupled 13C NMR spectrum of an alcohol C5H12O consists of four resonances. This observation is consistent with which constitutional isomers below? OH CH3 CH2 CHCH2CH 3 I CH3 CHCH2CH 2OH CH3 III OH CH3 CH2 CH2 CHCH3 II CH3 CH3 CCH2OH CH3 IV (circle answer below) only III I and IV only IV II and III (I) The major alkene product in the acid-catalyzed dehydration below will be (circle answer below) CH3 CH3 CHCHCH3 OH H + CH3 CHCH=CH2 CH3 CH3 CH3 C=CHCH3 CH3 CH2 CH2 CH=CH2 CH3 H2C=CCH2 CH3 (-H2O) (J) If the relative reactivities of different H in the free radical chlorination reaction are 3o-H/2o-H/1o-H = 6.0/3.0/1.0, the expected relative yields of the monochlorination products in the chlorination of butane will be (circle answer below) [1-chlorobutane]/[2-chlorobutane] = 1.0/2.0 1.0/1.0 2.0/1.0 3.0/2.0 Chemistry 322aL/325aL Final Exam (5) Contd. -10- Name_____________ (K) Free radical halogenation of alkanes proceeds fastest with (circle answer) F2 Cl2 Br2 I2 (L) Indicate all of the following reactions of alkenes that are stereospecific anti-additions. hydroboration I oxymercuration III bromohydrin formation II hydroxylation with cold KMnO4 IV (circle answer below) I and III II and IV II and III III and IV (M) Indicate all of the following reactions of alkenes that give anti-Markovnikov addition products. hydroboration/oxidation I HBr (peroxides present) III acid-catalyzed direct hydration II oxymercuration/demercuration IV (circle answer below) I and III II and IV II and III III and IV (N) Added ZnCl2 promotes the reaction of ROH and conc. HCl by acting as a (circle answer below) nucleophile. Lewis acid. free radical initiator. Lewis base. (O) An ether that is currently widely used as an additive in gasoline, but will be discontinued in the future because of environmental and health concerns, is (circle answer below) H2C O CH2 CH3 CH2 OCH2CH 3 CH3 OC(CH3 )3 O Chemistry 322aL/325aL Final Exam -11- Name_____________ (6) (15) Answer the questions below. (A) (9) Optically pure (100% ee) 2-octanol ([a] = -10.3o) with an oxygen isotope label is reacted by the scheme shown below. From the information given, provide detailed stereostructures for A, B and C and give the specific rotation of product C on the line below the box. Also describe the stereochemistry of each reaction as retention, inversion or racemization inside each shadow box. Note that product C is produced in 100% ee form. C6H13 H C CH3 2-octanol [a] = -10.3o 100% ee (i) NaH 18OH (ii) CH3 CH2Br A [a] = -19.5o 18 O retained in product CH3SO 2Cl amine base NaOCH2 CH3 B 18 C 100% ee [a] = _______? No 18O in product. C9 H20O3 S O retained in product (B) (6) Butyl alcohol is converted to butyl bromide under the reaction conditions shown below. Draw a detailed plausible mechanism for this transformation showing all key intermediates. Use the curved arrow formalism. CH3CH 2CH2CH 2OH NaBr conc. H2SO 4 heat CH3CH 2CH2CH 2Br Chemistry 322aL/325aL Final Exam -12- Name_____________ (7) (20) The free radical photobromination of alkanes with different types of H is a highly selective reaction, as shown in the reaction of propane where the product mixture is 2-bromopropane/1-bromopropane = 160/1. CH3 CH2 CH3 + Br2 hn 40oC vapor state CH3 CHCH3 + CH3CH 2CH 2Br Br 160 : 1.0 (A) (2) Calculate the relative reactivities of the two types of H (R2-H/ R1-H) on a per H basis from the observed product mixture. Place your answer in the box. (B)(8) Provide below the two propagating steps for the reaction that produces the 2-bromopropane product, and calculate the standard enthalpy change for each step using the available homolytic bond dissociation energies (BDE). Also, write out the net overall reaction and calculate the standard enthalpy change for this overall reaction. CH3 CHCH3 H -95 CH3 CHCH3 Br -68 Br-Br -46 H-Br -88 R2-H /R1-H BDE in kcal/mol Propagation Steps (1) DHo (2) DHo overall reaction DHo Chemistry 322aL/325aL Final Exam (7) Contd. -13- Name_____________ (C) (6) Complete the diagram below that describes the enthalpy change during the propagating step that is the rate-determining step. The horizontal line in the diagram represents the starting state with a relative enthalpy of zero. Assume a reasonable value for the enthalpy of activation (DH ) (essentially the same as the activation energy, Ea, in Arrhenius rate theory) based on the standard enthalpy change for the RDS. Clearly show the reactants and products for this step in the diagram. Identify the transition state and draw a structure for the TS. Provide a numerical estimate of the energy barrier. kcal/mol +10 Relative Enthalpy 0 -10 progress of reaction (D) (4) Explain the selectivity in this bromination reaction given the information that the BDE for the primary H in propane is -98 kcal/mol. Refer to the energy diagram above in your answer. Chemistry 322aL/325aL Final Exam -14- Name_____________ (8) (10) One of the key features of the synthesis of alcohols from alkenes by the hydroboration-oxidation sequence is the stereospecificity of the oxidation reaction, where the hydroxyl group replaces the borane group with retention. Explain this stereospecifiicity in the example below by sketching a detailed mechanism as a series of steps that show key bond-breaking and bond-making processes. Use the curved arrow formalism. H BH2 CH3 H HOO- +Na NaOH, H2 O H H OH CH3 Chemistry 322aL/325aL Final Exam -15- Name_____________ (9) (25) The table of reagents below may be helpful in answering the following questions. You are not limited to these reagents in designing your syntheses. Also be sure to include common solvents and acids and bases, as needed, in your syntheses. Do not show mechanisms but each step in your synthesis (reagents and products) must be shown as a separate equation. Table of Selected Reagents HBr HCl HI SOCl2 PBr 3 Br2 CH3SO2Cl H2/Pt H2/Pd(poisoned) NaBH4 NaNH2 NaH NaOEt KOBu-t NaOH Hg(OAc)2 KMnO4 O3 BH3.THF H 2O2 (peroxides) (CH3)3SiCl/amine base MMPP (magnesium monoperoxyphthalate) You may use other reagents as well in your syntheses. (A) (15) Provide a reasonable synthesis of A from 3-methyl-1-butene by way of the alkyne shown below. CH3 CH3 CH3CHCH=CH 2 CH3 CH3CHC CH3 CCH2CH 2CHCH3 CH3CH H C C O CH3 CH2CH 2CHCH3 H Any needed reagents may be used, but the only source of carbon compounds is 3-methyl-1-butene. A (as a racemic form) Chemistry 322aL/325aL Final Exam -16- Name_____________ (B) (10) Provide a reasonable synthesis for one of the following two transformations. Do not work both. If you work both and do not indicate which one is to be graded, only the first one will be graded. (i) CH3 CH2 CH3 CH3 CH2 CH2 OCH2CH 2CH 3 Any needed reagents may be used, but the only source of carbon is the starting propane. (ii) CH3CHCH2CH2Br + HC OH (as a racemic form) CC6H5 CH3CHCH2CH2 C OH (as a racemic form) CC6H5 Any needed reagents may be used. ...
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