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322af01_e2_key - CHEMISTRY 322aL/325aL Please Kt j EXAM NO...

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Unformatted text preview: CHEMISTRY 322aL/325aL Please Kt j EXAM NO. 2 Print Last Name OCTOBER 10, 2001 ‘ First Name SSN TA's Name Grader ,(1) (15) __ (2) (20) __ (3) (10) _ (4) <20) __ <5) (15) _ <6) (10) _. , (7) (10) __ Lab Day & Time (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) (A) (10) For the acid-base reactions below, supply the missing structures within the boxes according to the descriptive terms below the boxes. (See information in the Appendix, as needed.) Also, where there are lines below reactants in a reaction, identify the chemical species as Lewis acid or Lewis base, according to the produ-ts produced. C o “”sz Wf Q (i) CH3CH20H + NaH ——> n It f conjugate -acid conjugate base 9 ,1: (ii) CH3CH=CH2 + HF _-_> [email protected] + F mmmaqu NH; + (HQ fig'c‘dlfléc conjugate acid conjugate base +3 w y; H 89 __.-__. . “w E m7. conjugate acid conjugate base” W:fi ((3.; Ma 9 (v) CH3CHZOCH2CH3 + 31:3 F3 Gum CHCH CHCH . W Mfd 3 269 2 3 W(M (iii) CH3CEC-H + NaNHz ——‘——> (B) (3) For equations (ii) and (v), show all the bonding changes using the curved arrow formalism with the structures below. Add nonbonding electron pairs to the structures as needed for the curved arrow formalism. 69 (ii) CHBCH=c/Hz_>H? CH3CHCH3 + 1: ”/‘\ F3 (C) (2) In equation (v) above, the nucleophile is K "N and the electrophile is Min. . Q ( Shu chutes. OK lurex mA I Chemistry 322a / 325a ~3- Exam No. 2 (MO) 7 “LA (A) (15) Provide IUPAC approved names for the structures, or provide structures inside the boxes r h , t d b 1 . ort e names as reques e e ow OH I fi- L ’ ”(2 ,LI- _ CH3CH2QHCHZQHCH3 CquHCHzéHCHB [Z A 4- gt c 2. CH3 CH3 CHch3 2H“¢"""~*“\jlbt:¢ggg fi-méfiblc hqggmol W Name CH3CH2CHC1CH=CH2 1 fi if “C / -L/ - 3 ~C\\loro -- \- Eemflxg oeL \ HSCHzc H CH *3 3-penten-2-ol (B) (5) For each of the constitutional isomers of C7H16 in the box below, indicate the number of different groups of equivalent H. Exam . 1e usin - - ro . ane: CH3CH2CH3 2 CH3C|HCH2CH2CH2CH3 L (CH3)3CCH2CH2CH3 _Lli_ CH3 CH3CH29CH2CH3 5 CH3CH2CH2CH2CH2CH2CH3 it— CH3 Chemistry 322a / 325a -4- Name Exam No. 2 (3) (10) (A) (5) Select all the reagents from the list of choices that will accomplish each chemical ' below. Place oura we sin' theb . transformation y ns r Slde oxes 3 p fi_ ‘— fl 0.. 1"“ \QNE3 NuHim itkW‘A L‘H‘d“ 0‘) m WM; CH CH CEC-H ......................... CH CH csc': Na+ ____ é — M 3 2 ‘> 3 2 v“ n M. W V‘ 1/ CH3COZ’ +Na in ethanol Na+ NHZ' in liquid NH3 A N r 1 7 a 0 choices: CH3CHZO' +Na in ethanol NaH in diethyl ether . .® C ”sq’rz ”g NH3 ------------------------------- » Na+ 1in 7/ choices: NaH in diethyl ether CH3CHZCEE: Na+ indiethyl ether CH3CHZO' +Na in ethanol, CH3CI:122 Na" in hexane (B) (5) You have a mixture of two organic compounds, 4-methylphenol and cyclohexanol. Both are low melting solids with very limited solubility in water (less than 3 g per 100 mL). However, they have very different acidities as shown below. pKa = 10.2 PKa = 18 mp 35.50 C mp 240 C CH3 4-methylphenol cyclohexanol You prepare a strong basic, aqueous solution of NaOH in water. When you add the mixture of 4-methylphenol and cyclohexanol to this basic solution and stir briskly, one of the compounds dissolves completely. (A) (2) Which compound dissolves? - l- \ mm (B) (3) Write a chemical equation inside the box that describes the chemical change that results in one compound dissolving. Chemistry 322a /325a -5- Name Exam No.2 g M (4) (20) Circle the correct answer for the following statements or uestions. (A) Which of the following is not a Lewis acid? circle answer H3O+ rAlCl3 @ BECIZ (B) The order of acid strengths (strongest to weakest) for the compounds below is circle answer CH3CH2CH=CH2 CHaCI—IZCHZCHZOH CH3CH2COOH I>II>III II>I>III I H 1“ II>III>I- (C) The order of base strengths (strongest to weakest) for the following anions is circle answer £le CHso I" éH3 I>II>III>IV I H m N IV>II>I>III I>IV>II>III (D) Which of the acids below will have the weakest conjugate base? circle compound below CH3COOH ClCHZCOOH CIZCHCOOH pKa = 4.75 pKa = 2.81 p1<a = 1.29 C13CCOOH Ka = 0.66 (E) Which of the following is the strongest acid? circle compound below + H20 CH3OH2 CHSQCHS pKa =15.7 pKa = -2 pKa = -3.5 (F) The standard free energy changes (AGO) for the dissociation of two acids, HX and HY, are given below. (1) H-X + H20 :12: H30+ + X' AG°=+3.5 kcal/mol (2) H_y + H20 ‘—__—_'- H30+ + Y' AG°=-1.5 kcal/mol According to these values, (circle answer below) ~the acidity constants for both acids are greater than 1, but H-X is the stronger acid. acidity constants for both acids are 1 than 1, but H-X is the stron er acid. -the aci 1 constant or H-Y is greater than 1 and it is the stronger acid, while the acidity constant for H- ‘ s than 1 and it is the weaker acid. -the acidity constant for H-X is greater than 1 and it is the stronger acid, while the acidity constant for H-Y is less than 1 and it is the weaker acid. Chemistry 322a / 325a -6- Name Exam No. 2 (4) Contd. 2* £46k (G) The following diatomic molecules that are "infrared active" are NEN 'Br-Br H-I H-H (circle answer) N2 and HI N2, BIZ and HI only BIZ (H) The heats of combustion of several isomers of C6H14 are shown below. According to these values, CH3CH2CH2CH2CH2CH3 (CH3)3CCH2CH3 CquHqHCHa CH3CH3 AHgomb ‘995 kcal/ m01 '9915 kcal/mol -993 kcal /mol (circle correct answer below) -2,2—dimethylbutane is the least stable and hexane is the most stable isomer. -2,3-dimethylbutane is most stable and hexane is the least stable isomer. - - is the most stable and -dimeth lbutane is the least stable isomer. (circle answer below) H H H H H flag CHtébf: CH H3 CH3 H H H3 H CH3 CH3 H H H H H (I) A gasoline with a performance in the internal combustion engine equivalent to a mixture of 80% "isooctane" and 20% heptane is given an octane rating of \ (circle answer) 20 60 100 Chemistry 322a / 325a -7— Name Exam No. 2 (5) (15) The acid strengths of acetone (a simple ketone) and propane are shown below: (3 K3 = 1.0x10‘20 ' (R CH3CCH3 + H20 H30* + CH3CCH2' acetone Ka <10’5° + + _ CH3CH2CH3 + H20 H30 CH3CH2CH2 propane (A) (10) Cemplete the free energy diagrams below for the two equilibria above by (i) identifying the reactant and products states for Diagrams A and B by writing RS or PS inside the circle next to the state, (ii) drawing an arrow from the reactant state to the product state and writing the symbol for the standard Gibbs free energy change (you do not need to calculate the value), and (iii)_providing the correct structures for the reactant and product states for each diagram inside the boxes below or above each state. >3 OD H U S: Q) Q) 0) H H-( CHCH CH 4» \+ o (B) (5) Use resonance theory to explain the difference in acidity between acetone and propane. U onance structures in your explanation and refer to your free energy diagram above. Be E i concise! "" "' ' ' leu-vuzs +kx ammo“ 0‘? PTOPCK‘MK \S «\ocatr-de («V’ba-«iokg H 63) ‘ __ L ,0. q.) :9: are; 5 (5" caged—t1 é» CHsC-ZCHL mac-2m; [W mm“; HM RLSOMQLtk S't‘aAfilrzgg W azure-w. «mom \m‘t-‘w. {Pr-odu‘i‘l: Chemistry 322a / 325a -8- Name Exam No. 2 (6) (10) Answer the following questions about the conformations of simple alkanes. (A) (2) Define "torsional strain" using ethane as an example. bes‘D’Au/\ s—k—vfim \S +\\L_ S+mt~x {Nu-g7 \x‘h‘OJt-«aJ i») edrpsd' H as 1K ‘ir‘vxt eclipsci Can/\(orm‘fio‘m 090.qu W J-L |+ u \+ H u ' 'PH 7-. :- W’fflRt—t ’ H “L “I: 5‘3“ ‘ u u HS—lfligflcfiia h‘k~-CIXK echpScd "i‘DV‘S‘IOMoJ $—+r~oJM 2) For the al ane below, identify the carbon-carbon bond with the highest barrier to rotation. Place your answer on the line as Cm-Cn where m and n are the positional numbers. 1 2 3 4 CH3-CIH-CH2-CH3 E 5 “CB CH3 C-C with highest barrier to rotation 5 (C) (4) Draw gauche and anti conformations for rotation around the C2-C3 bond in butane (CH3CH2CH2CH3) by completing the appropriate Newman projection formulas below. Write the name of the conformation (gauche or anti) below the completed Newman projection formula. Use only two of the four Newman projection formulas below. CHB CH3 “is ‘4 :éf ” g‘ n? H H H / \ H QaucLe A144 (D) (2) Which conformation, gauche or anti, is more stable? What is source of the energy difference between the conformations? TiAg CL'Hf—i (Owkr NKL-HOM \S. MOP! SM‘g Timm— vs S‘Ivvtg S-Hojex 4mm +i~k N—‘VLYi Groups \’Y\'\’\/\L Gmuckn ComfivMa‘i—i 0%. l I ,. C. 9 \l" 4000 3600 3200 2800 2400 2000 1800 1500 1400 1200 1000 800 600 400 . . Moo-1'1. ‘ . . -- .~.a..-...'ar....._.. Chemistry 322a / 325a Exam No. 2 Name («£464 40K 426%]; (7) (10) I am a hydrocarbon named A. My infrared spectrum is shown below. I react with hydrogen gas over a platinum catalyst to give compound B (IR spectrum below). Compound B has a symmetrical structugg with only primary and secondary H. Combustion of one mole of compound gives 6 moles of C02 and 7 moles of H20. .3 c is , symmetrical f combustion of structure with one mole of B o tertiary H . M” . { / IIIIIIIIVI 2.1"“...- Wavenumber. cm'| Transmittance, % (microns) ...
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