chem322a--exam 2 %28sp. 04%29

chem322a--exam 2 %28sp. 04%29 - Kc \/ CHEMISTRY 322aL...

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Unformatted text preview: Kc \/ CHEMISTRY 322aL Please EXAM NO. 2 Print Last Name MARCH 1, 2004 First Name USC ID No. TA's Name Grader v (1) (15) __ (2) (15) __ (3) (10) __ (4) (20) __ (5) (15) __ (6) (10) __ (7) (15)— (100) first letter of last name I will observe all the rules of Academic Integrity while taking this exam. Chemistry 322a/ 325a -2- Name Exam No. 2 (1) (15) Answer the following questions about the acid-base reaction shown below. Cyclohexar‘l01 sodium phenoxide pKa = 16 (A) (2) Based on the pKa values, will the above acid-base reaction spontaneously proceed left to right, or right to left? m §M+ +1: \‘L'Q -\— (B) (2) Is the standard Gibbs free energy change (AGO) positive or negative for the above reaction when it proceeds left to right? E o s t+\V L (C) (4) Draw a free energy diagram for the above reaction. The vertical axis is relative free energy, and the two states (left side and right side of the arrows) must be correctly placed relative (but not quantitatively) to each other in the diagram. Use an arrow to show, and label, the standard free energy change (AGO) in the diagram for the above reaction that l proceeds left to right. Ago \5 puertw; 3 3-: OJ t: “J U Q) 3-. LL. 0 > .5 (6 fl U m Chemistry 322a/ 325a -3- Name Exam No. 2 (1) Contd. (D) (2) Based on the above pKa values, which oxide is the stronger base ggnoxide or cyclohexoxide? (“Manama o ./ Which oxide is the more stable a318, phenoxide or cyclohexoxide? Q‘Il'hoigél (E) (5) Use resonance theory to explain this difference in base strength and stability of the oxides. Hint, consider a Kekule’ or Lewis structure for the phenoxide ion. Then use carefully drawn resonance structures in your explanation. An energy diagram is not needed, but your explanation must be clear. Phaehoaqclo. \s Mort SSW-\o‘u max Cyclolnu‘omdk \O’M~ ER \s Cc \OC¢\\'2_Ld OXYee’m CL'KIO’K- Thu—g C‘J‘K I ma «dig-hwyan rage—nervuq $+r~u¢+vt\: §>oxsthle , fl- . +\’V\ r—LSOWMKQ 4“ M3 SQVL roA C Dim-M‘x ‘D U C, K/ s+ru C‘rkms SJVO—b? Mic “FL; t“I hr; <1, OVar any gxnéh Luau: Straw-hurt— 556 Chemistry 322a/ 325a -4- » Name Exam No. 2 (2) (15) Answer the questions below. (A) (12) Provide systematic or IUPAC names for the structures, or provide structures inside the boxes for the names; as requested below. ’ CH3CH2§HCHCH3 H/C=C\H CH3 3 3* Nut-k3 \ —-'2— gen—had SSS—6 - Q\\\oro v~ " Hawtng A6 A. OH (\K CH5 / z'methyl‘z'CY-dOhexenOI 1-chloro-4-phenyl-2-pentyne (B) (3) Draw a detailed structure of isobutyl bromide in the box; (3)(10) In the boxes below, provide conformationally correct structural formulas as - requested. 6) H CH H3 CH3 a Newman PTOlECfion _f01’m‘~113 the most stable conformation the most stable conformation along the CZ‘Ca bond m bUtane for methylcyclohexane for cis-1,3-dimethylcyclohexane for the anti conformation any c {at r l] ',{;1,Z%WIFZ A3 I W» 0K Chemistry 322a / 325a Exam No. 2 (4) (20) Circle the correct answer for each question or statement below. (A) Which of the bases below could be used for the following reaction? CH3CECH + 13:" CH3CEC:' + B-H NH' CH co H c- H'h d 'd) (Cimleanswer) ‘ I I 1'1 8 2 ( 393 3 ( y IandIII III and IV I II III IV I, III and IV all of them (B) Which of the following solvents could never be used for the reaction in (A)? diethyl ether ( water \, liquid ammonia (C) In the oxidation of methane carried out under nonstandard state conditions, CH4 + 202 2H20 the enthalpy change is AH = -212 kcal mol'1 and the entropy change is AS = -50 cal K-1 mol-l. Which statement is true about the contributions of the enthalpy and entropy changes to the spontaneity of this reaction? (circle answer) hexane ——-——>COZ+ —Both AH and AS make favorable contributions to the spontaneity of the reaction. the s ontaneit of the r . ' o n -Both AH and AS make unfavorable contr' - on t - eaction. --AH makes an unfavorable, but AS makes a favorable contribution to the spontaneity of the reaction. (D) The order of acid strength (strongest to weakest) of the three compounds below is (circle answer) 111>11>1 I>III>II III>I>II + CH3CH2oH CH3COOH H H20 I II III (E) In 1,1-dimethylcyclopentane, there are -6 equivalent primar H and 8 euiv . ' a ent rimary '-‘ - uivalent secon nd 4 equivalent secondar H. qua ent primary , equ1va ent primary , an : equ1va ent secondary H. -3 equivalent primary H, 3 equivalent primary H, 4 equivalent secondary H, and 4 equivalent secondary H. Chemistry 322a / 325a —6— Name Exam No. 2 2 646 IV (4) Contd. (F) In the chair conformation of trans-1,3-dimethylcyclohexane, the number of gauche interactions (G) is 06 1G'@4G (G) The cycloalkane below with the greatest amount of angle strain is cyclopropane CYdObUtane cyclopentane cyclohexane (H) The conformational structure at the t0p of the 10.7 kcal/mol energy barrier during chair-chair interconversion of cyclohexane is OHM planar pure boat twist boat half chair (1) Among the three stereostructures below, 0 O n u H 9H 9H 9H HO' \CHZOH Ho' :;\CH3 HOCH'2 :2 ‘21-13 CH3 HZOH OH I II III -I an I] -I and III are the same stereoisomer. - an e e same 5 ere01somer. -I, II and III are all the same stereoisomer (I) The order of priority from highest to lowest of the three groups below for assigning (R) and (S) configurations around a stereocenter is (circle answer below) CH3CH2- H2C=CH- HCEC- I>II>III 11>111>1 I II III I>III>II Chemistry 322a / 325a Exam No. 2 (5) (15) Name (A) (5) Indicate whether t CH3CH2CCH2€¥ICOOH CeHs . Ami— CH x‘. 3 _<.‘-_A::9.~.l___ (B) (5) Provide a complete IUPAC n he following compounds are chiral or achiral on the line below the structure. For a chiral structure, identify the stereocenter with an asterisk (*). CH3C;‘l-ICH2CCH2CH2C1 1 m4 ClCHZCH=CH2 W (L L,\n K V0.5 Z ame for the compound below. Your name on the line must properly identify the stereocenter. In the box below, draw a stereostructure of the enantiomer of the compound below, and provide a complete name on the line below the box.. CH=CH2 @( R\' E'C—\\\oro—-\—\: x:th (C) (5) Identify each pair of structures below as constitutional isomers, enantiomers, or the same compound. €1.13 CH3 2H3 2H2CH3 CH3(E\OH Hcfcg\CH3 H 2 OH H 2 0H {1 fi CH2CH3 CH3 1 ‘1 ° 0 U A M H 11 CH 2 : / C—HzCl-IzCél-ls Cems‘kI-k-u-Hom;\ \somrs C1 SCLML Co mgr: u m a VH3 :KD/U—Ig "'7 CH ""0; ”CH3 H H C0~x§i§iu 33‘ Q 395 \ pom! F5 Ilh. Chemistry 322a/ 325a -8- Name Exam No. 2 (6) (10) Compounds A and B are constitutional isomers of C6H14. Answer the questions below. (A) (7) Isomer A may be synthesized by the following scheme from the hydrocarbon C4H6. Provide correct structures inside the boxes below. NaNHz Q4304an c\-\ liq NHa C4H6 (an alkyne) catalytic hydrogenation excess H2 Pt A C6H14 C6H10 (6 equivalent primary, 4 equivalent secondary, and 4 equivalent secondary H) ( 6 equivalent primary and 4 equivalent secondary H) (B) (3)Isomer B is directly prepared from an hydrocarbon C6H12, as shown below. Based on the information below, provide correct structures inside the boxes. H H a Newman projection formula for B (an alkene with 12 equivalent H) Q MK—e wk, Chemistry 322a/ 325a -9- Name Exam No. 2 ' (7) (15) The heats of combustion of four isomeric dimethylcyclohexanes were measured more than 50 years ago as v (I) cis-1,2-dimethylcyclohexane: -1248.0 i 0.4 kcal/mol (II) trans-l,2-dimethylcyclohexane: 4246.8 _-_t-_O.4 kcal/mol (III) cis-1,4-dimethylcyclohexane 4247.4 +_0.4 kcal/mol (IV) transl,4-dimethylcyclohexane 4245.8 i 0.4 kcal/mol (A) (2) Write a balanced equation for the combustion reaction of C53ng in the box: C8H16 + \sz—‘sgcvl ~\— 8 H29 (B) (4) According to the heat of combustion data, what is the relative stability order of the dimethylcyclohexanes I, II, III and IV? Rank them from most to least stable, Most stable E> E > El: > 1 least stable What important feature of the combustion reaction allows a direct measure of the relative stabilities of the isomeric cycloalkanes from the magnitudes of the heat released? A Commo'rx Qvosluct s-‘ro—‘tk (QCOL—t 8H;O\ quot-9% “Flu. AQC V¢\UL% +0 91+- +\u_ Kant—\SO‘Q’ We s+¢r+vyxs $‘Hfl15‘ (C) (6) Carefully draw structures of the most stable conformations of trans—1,2- and trans— 1,4-dimethylcyclohexane in the boxes below. trans—1,2—d' ethylc clohefineék ns-l, dimethylcyclohexa \ or MA OT; ‘ clout?) ' WM. /\ (D) (3) Explain the relative stabilities of the isomers n terms of strain energy differences in the structures. E ‘S More 5*WE\€ E: \DQ(O~\,\$Q \s W W E, OWL—cm \S S! aim/gag. Tl»!— O-hq @- \s du; 4:79 W Lt ’l‘l—Oa CH Grodlbsl étémw ./ v (‘7 H C963 5 ...
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This note was uploaded on 03/01/2008 for the course CHEM 322AL taught by Professor Jung during the Spring '07 term at USC.

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chem322a--exam 2 %28sp. 04%29 - Kc \/ CHEMISTRY 322aL...

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