322af05_e2_key - CHEMISTRY 322aL/325aL Please SQ— i ‘...

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Unformatted text preview: CHEMISTRY 322aL/325aL Please \ SQ— i ‘ EXAM NO. 2 Print Last Name OCTOBER 5, 2005 First Name USC ID No. TA's Name Grader (1) (15) __ (2) (10) ___ _ (3) (15) ___ __ (4) (10) ___ __ (5) (20) __ __ (6) (10) __ .— (7) (10) __ _-_._ (8) (10).__. __ (100) Lab Day & Time _I I will observe all the rules of Academic Integrity while taking this exam. Chemistry 322a /325a -2- Name Exam No. 2 (1) (15) Use information in the Appendix, as needed, to answer the questions below. (A) (9) For the following acid-base reactions, provide the missing structures inside the boxes according to the descriptive terms below the boxes. Where metal ions are shown, be sure to include them in your products. Draw an arrow inside each small box to show the direction of the spontaneous reaction, using information in the Appendix. spontaneous direction 1, “c L CH3CH20' Li+ + HC= CH CH 3QH 20H + k 0,) conjugate acid conjugate base spontaneous L ' d_irection O H + erM conjugate acid conjugate base spontaneous direction ‘ 5H (9 I + CH3CCH3 + H2O H30 conjugate acid conjugate base (B)(4) Add the missing non-bonding electron pairs and any missing formal charges to the structures below. Use the curved arrow formalism to shown the movement of electron pairs. On the line below each reactant, entify the compound as a Lewis agd or L base. “(if m/OIV u, u; Cl: @915} CH3-Cl-A1-Cl (C) (2) Provide the order of base strength (strongest to weakest) of the oxygen anio. below? order of base strength 11:, > W > .3: strongest weakest Chemistry 322a/ 325a -3- Name Exam No. 2 (2) (10) Carefully read procedures (A) and (B) below, before answering the questions. (A) (5) A mixture of 10 g of phenylethynyllithium (I) in 50-mL of benzene (II) is added to 100-mL of water in a beaker and stirred vigorously. When the stirring is stopped, two liquid phases separate. The lower phase is aqueous and the top (lower density) phase is hydrocarbon material. @5 6:: Li” © 1 II (i) (2) What is the chemical composition of the top hydrocarbon phase? Provide a structural formula or formulas of the hydrocarbon material in the top phase. 1- ML (\01 «- @jcacbt (ii) (3) Is the lower aqueous phase acidic, neutral or basic? Explain with a chemical equation. Bats tC. ‘ 1 /—> G 1 “£96 ® Q) C H C: - hug 7/ CGHS‘C—E'LC‘Lr + H10 #9 s r -CH *- LIGH ‘7 1% ‘1 ox- 3 M“? L pk“? (B) (5) A 100-mL solution of pentane (bp 36°C) contains 10 g of triethylaznine (bp 893°C) and 10 g of cyclohexane (bp 807°C, mp 65°C). CH3CH2CH2CH2CH3 (CH3CH2)3N O . pentane triethylamine cyclohexane J When HCl gas is bubbled into the pentane solution, a white precipitate immediately forms that is easily separated from the pentane solution by filtering. The white precipitate is soluble in water. (i) (3) What is this white precipitate? Provide a chemical equation that describes how it is formed. © 6 (CH3CHQJ1N: .\_ HQ( _———’> CCHBQHQKNH Q C/ . MAM _ (TM!— anH-L 9331‘ \S +r‘. L‘k-ln ammox} u M QLJ o P:in (ii) (2) When the filtered pentane solution (the filtrate) is gently heated, the volatile pentane boils away rapidly leaving a liquid residue. What is this residue? uicL I‘Lgriuz ts +LQ \WTS thr \307 LT’N‘D‘ Cx(clok2 sake. _._._._ ._ \\ Chemistry 322a / 325a -4- Name Exam No. 2 (3) (15) Answer the questions below. (A) (12) Provide systematic or IUPAC names for the structural formulas, or provide structural formulas inside the boxes for the names, as requested below. L V“ H 3m 3~c(..-q-1-~yM—L CH3CH2CECEHCH2CH3 __ b __ ““1 +‘l'1fi c>~\ r0 3 e K &+\’w‘_CH2CH3 hon" \rc Or 3- 1~C\¢c_l0?1‘r\ 3 «1+k1lc7:\opam‘\' —'L-—¢z’h~— \»-a \ trans—3—penten—2-ol 1,3,3—trimethylcyclobutene /‘ 1%,:th (B) {3) An alkene with the molecular formula CSHm is capable of existing in cis and trans isomeric forms. Draw a structural formula of one of the isomeric forms in the box below and provide the correct IUPAC name for that isomer on the line below the box. “ /“3 Chemistry 322a/ 325a -5- Name Exam No. 2 (4) (10) The acidities of methylarnmonium chloride (I) and anilinium chloride (II) are given below as values of pKBH+, where BH+ is I or II, the conjugate acid of the amine base, methylamine or aniline. K = 10.66 p sir CH3NH3+ C1. + H20 CH3NH2 + I'I3()+ + C].- I methylamine K = 4.87 P sir NH3+C1' + H20 NHZ + H3O+ + Cl' 1 II aniline 29(A) (2) Which is the stronger acid, I or II? P- ich is the stronger base, methylamine or aniline? «Hid! <3me n I 4/ 6&4)” W on (B) (6) Complete below the Gibbs free energy diagrams for the o acid—base equilibria shown above. The two conjugate acid starting states are set at the same relative free energy level for convenience in comparing the two systems. While your diagrams do not need to be drawn to scale, the final states the free mtates) must be positioned correctly relative to each 0th and the startin st '- f r ‘ r“ , es Q ' x 46 mf‘J ‘ W e W um ./ ( . Iv; I CH3NH3+ c1'+ H20 11 CeHs-NH3+ c1'+ H20 relative Gibbs free energy (C) (2) When either methylamine or aniline is added to an hydrochloric acid solution, does the resulting acid-base reaction have a positive or negative free energy change? AC ‘35 *113 Lt‘ V1. @M‘IL (P15 f‘vwé' M’Z‘fi‘m“ Chemistry 322a / 325a -6- Name ’ Exam No. 2 2 M F__________. (5) (20) Circle the correct answer for each question or statement below. (A) The correct descriptive terms for the reactants below are + .- 29-3123 CH3CCH3 CH3CCH3 + BF3 A B (circle answer below) A, electrophile / Lewis base and B, nucleophile / Lewis acid ' ' ' nucleo hile / Lewis base A, nuc eop ew15 acid and B,electrophi1e / Lewis ase (B) A solution of the reagent methyllithium (CH3Li) is sold commercially and widely used in organic synthesis. Which of the following solvents may be used with this reagent? (circle answer below) acetone water acetonitrile hexane hmnl water .i PKa 19 15,7 25 >50 acetonitrile and hexane acetone and water (C) For the reaction between nitrogen and hydrogen to produce ammonia (shown below), the standard enthalpy change is AH° = -21.9 kcal and the standard entropy change is AS°= -47.26 cal/K. Which statement below is correct? N2(g) + 3N2(g) 2I‘ll—13(5) -Both the standard enthalpy change and standard entropy change make favorable contributions to the spontaneity of the reaction. -Neither the standard enthalpy change nor the standard entropy change makes a favorable contribution to the spontaneity of the reaction. ~Only the standardrentropy change makes a favorable contribution to the spontaneity of the ( -Only the standard enthalpy change makes a favorable contribution to the spontaneity of the reaction. (D) The pKa values for the three carboxylic acids below indicate CH3CH2CH2COOH HCECCHZCOOH CH3C ECCOOH I II III pKa 4.8 3.32 2.59 < circle correct statement below) -the strongest acid is I and the alkynyl group is electron donating. -the strongest acid is I and the alkynyl group is electron withdrawing. -th ' ' ' is electro natin . -the strongest acid is 111 and the alkynyl group is electron withdrawing. Chemistry 322a / 325a -7— Name Exam No. 2 (5) Contd. (E) In each pair below, the stronger base is _ _ _ (circle answer . - - CH3O‘/CH3NH CH3CH2/CH3NH I CH30' II CH3CH2 I 11 I CH30' II CH3NH I CHsNH II CH3NH (F) An alkane C6H14 that has only two different groups of chemically equivalent H is hexane 2-methylpentane ( 2,3—dimethy1butane ) 2,2-dimethy1butane (G) How many different constitutional isomers are there for C4H9Br? (circle answer) 2 3 <9 6 (H) The name of the alkane shown in the Newman projection formula below is (circle answer below) H2CH3 2,,3—dimethylbutane 2,2—dimethylbutane CH3 (’ 2,3—dimethylpentane )2,2-dimethylpentane (1) During a 360°rotation around the indicated C-C bonds in LII and HI below, there will be three equivalent energy barriers in l l 1 CH3— CHZCHZCE‘TW (CH3)2CH '— CH3 CH3CH2—CH2CH3 I II III (circle answer) onlyI only 11 I and III (J) In the combustion of the following cycloalkanes, the least amount of heat per CH2 group is released with (CH2)n + 732— no2 nC02 + nHzO + heat (circle answer) cyclopropane cyclobutane cyclopentane Chemistry 322a / 325a -8- Name Exam No. 2 (6) (10) The heats of combustion for three isomeric cycloalkenes (C6Hm) are given below. : I st fHa I II III -896.0 -900.0 -897.0 heat of combustion, AH:omb (kcal/mol) (A) (2) What is the stability order of I, II and III according to the heats of combustion? 20f 0 Moststable I > I“ > H leaststable (B) (2) Complete and balance the equation for the combustion reaction of C6H10. '—"———" 0" Aooh‘ti C6H10 +8502 GCOL "" SHLO W ‘ (C) (6) Draw diagrams below showing the enthalpy changes associated with the combustion reactions of alkenes 1, i1 and 111. Be sure to clearly identify the starting and product states in your energy diagrams. Your diagram must Show why the heats of combustion provide a measure of the relative stabuities of the isomeric alkenes. ‘ ' CH3 CH3 l com/é @ +‘ $107— \ — o ____,._____ ‘/\[S_¥le:07_ + 82- 2' 3 relative enthalpy BICMSL 6Q ‘F-kz “MN“ PPOAU¢+ s'f‘ofl‘k] 'k—kL k1: (IV 0.32 cl 51—5 +\‘\3\ [‘k\a.'+‘(\/I~ €‘n‘\'\’\d\P—\ 0Q +AQ SHF‘H’N SH‘HS , 1 La- Avg-9b...“ ”A Q M9,] \ ‘L c4r\~ [NAG—0.3K.) \‘L + K & [WKNKS [‘Y\ \re— 43 0“: AhwhfiDM ”‘9’ ”‘k1 KSDNBS.‘ Chemistry 322a/ 325a -9- Name Exam No. 2 (7) (10) Answer the questions below. (A) (6) Assign the proper hydrocarbon structures from the following choices of I - VI to each of the three infrared spectra A, B and C in the Appendix. Structure Choices for IR Spectra ©c— CH CH3CH2CH2CH2CH2CH2CH3 ©CH=CH2 11 I III CH3CH2CH2CH2CH2CH=CH2 IV CH3CH2CH2CI>ITCZ CCH3 CH3CH2CH2CH2CH2C E CH V VI Spectrum A V 1 Spectrum B l V Spectrum C H (B) (4) Explain why the hybridization state of the carbon atom (sp, sp2 or sp3) influences the C-H bond stretching frequency in the infrared. Which hybridization state for carbon has the highest frequent} for the C-H stretch? The equation describing Hooke's law is given below for reference. Calculations are not needed or desired in your answer. K v (5-1) = x, x c (speed of light) =<31E> m) A B A B where M A and MB are the masses of the C and H atoms and K is the force constant. SP-H‘lbrifitzLi Q, \'\0~é +\-\9\ hTfikL‘g—‘f‘ ¥bgim%(j($j $or +lnz Q—H §+r1+gk 3\/ HODKI(S law, -\——\,\._ LNiUQ’KQV $1Q¢WAg Owck “J" KK} a4A¢ "S’kk Wtfisib ”'9 +l\0\ QJrow5 Q3 SKOQ’LC STMQK +\~L “4-352 S arse. m $auvx0~ ) fig di-C-H T'LK‘V‘ 7cm$ULMCF¢s 0'; fix). C—r' SJn-«L‘Cbk ‘é’F 3?; S?Z “Ki SP3 by bt—Tclf‘LLA. C aro‘ ivxk J—O SLL‘IC‘A‘FL'flN-l‘ \‘Qvgm CoM‘l‘a-ul‘x‘s" .l’kx Chemistry 322a / 325a -10— Name Exam No. 2 (8) (10) Answer the following questions. (A) (4) There is a small energy barrier during the rotation around the C-C bond in ethane as illustrated in the diagram below. Provide the name of this energy barrier on the line in the diagram. In the two boxes, draw unambiguous Newman projection formulas of the conformations that exist at the indicated points in the potential energy diagram. rotation around C-C bond '—'> (B) (6) The conformational energy diagram for rotation around the C2-C3 bond in butane is shown below. Draw unambiguous Newman projection fomulas of the conformations at the indicated points in the energy diagram inside the boxes. On the lines below the boxes, give the specific names (not general names) of the conformations. >3 2? Q) s: Q) E E 3 8.. | — 0° 180° 360° (1/ rotation around C2-C3 bond“—> What is the energy difference AE due to? .S'l-t r'rc S Arm? ”W \L‘VVJ ‘9 "’\ ‘ A§~\.\a_ Ma 4‘4““ avoup; f.“ “ble SPAKCRL (Om rpm-AGO,” Va,“ 61 (— MJa—L\$ PtrQJLSfOM &'7\e r57. Appendix Infrared Spectra for Problem 7 Spectrum A TRANSMUTANCE 3000 2000 1000 TRANSMHTANCE 00 3000 2000 1000 TRANSMHTANCE 3000 2000 1000 ...
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