Chemistry 3A - Spring 2002 - Frechet - Midterm 1

Chemistry 3A - Spring 2002 - Frechet - Midterm 1 -...

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Unformatted text preview: Chemistry 3A — {$124M 13711‘3 '39P! _. Midis“ MiD‘T stem 1 ._ 5Plilir~lq "2.12m _ F11?- é c. treT Professor Jean Fre'chet Your full sir, _ _ February 23, 21.11212 Print yourt tiddle} ‘r'our StEi_ Please check the section number and name of yo __ 151 Margot Paulin f 1?1 Danielle Dube _ 131 Matt Pratt _ _ 131 Laurie Schenkel _ 4?1 Alex Kcllias _ _ 111 Cathleen Yong _ 411 Andrew Chi _ 121 Priya Sonik _ _ 421 Shahed Ghoghawala _ 131 Paul Furuta _ 431 Mike Slater _ 141 Zach Fresco _ 581 Jean Han _ 231 Aaron Stutz _i5?1 Clgnjen Miljanic _ 2T1 ‘y'anessa Sun __ 511 Joe Kwon _ 211 Jamey Kain __ 521 Catherine Chan _ 221 Laura finderson _ _ 531 Olga Fedin _ 361 Fleema Thalji _ 541 Jason Serln 371 Warren Wood [in not write in this box. It you are making up an l—grade. indicate the semester you took 31% _ and the Professor -— This exam has 1121 pages; make sure that you hays them ail. Ptease be sure to use the yer}: useful data given on page to. We will only grade answers that are in the designated spaces. Pin do your scratch work on the backs of the exam pages. Write only answer to each problem; multiple answers will receiys no credit. one of them is correct. Note: This examination runs for a total of so minutes. No guestic be answered by proctors after the exam begins. Please write leg ambiguous or messy answers will receiye no credit. is} 23132 J.M.J. Frechet. Berkeley. CA -..E.'-2oo2.l. Frechet. Berkeley Chem. 3A 2flfl2 Midterm Exam #1 Page 2 of 10 ‘1- t 15 POMS} {a} The elemental analysis of an unknown alcohol reyeals that it contains 5on oxygen. 3.5% carbon. and 12.5% hydrogen. What is its empirical formula {show your calculation}. Use the following atomic weight yalues: t3 = 12. H =1. 0 = ‘lfi. 1’ r V—E? E it “'Fttit'fti': W -— taste iixsisy-l'l'l a J} D l _ Mn'lazi-j _ grgflflu PAL 1—5.1, H W ll gilt“..er [a : r.}_";lt} e “W21: {LED 1]": Icy-501” f IL — - ~ ‘ '-' 0.1“; ' f}1i-ijt—tfi- l J—zclnes “U 3-: onfiw‘ I O I I Answer: C Mr H: W152} 2:11‘JI-yr: '13::I {b} Write Kekule structures for three resonance forms of [CH2NCH2]+ Show the location of the charge. circle the resonance form that contributes most and explain your choice. H a. _ I ' “61/- e ‘1 ~. [It I - f” " G) Lil —L x H C.‘:— N: 1% H ’ [his a “H .z .._:r e ,. l+ ' — N - C H ” \ ' "we? wtt trill-F {'11—‘1th f a LI' 3+ 5 {c} Draw the Lewis—dot structure of the methylene dianion CH2} as well as a 3-D structure showing all the orbitals and state the hybridization of the (3 atom in this oianton. ' .r .I" I gr" I; .r' lflfil 3—D with orbitals Lewis-dot ozone J. Frfichet. Berkeley Chem. 3A EDDIE Midterm Exam #1 Page 3 of ’10 2. { 1t] points} Name {IUF‘AC} or drawr as appropriate. the following molecules. l- brow-pa :f-thfl'4‘W-E‘T‘Ff1td9mrlt? L115“ 1355* dtmfithyt birocio i: ‘i'r .10] Mr. or. e pie—l —o‘nIoro—E-ethyloyolohexane {M oat etaole ohair conformation} id} t.1",Tutrimethyloioyolo[2.2. ‘l 1heptane lei 2,2-oibromo—3~oyo|opropy|nonane to zoom. Frechet. Berkeley Chem. 3A 213132 Midterm Exam #1 Page 4 of “ID 3. t 14 points] {a} What is the SHAPE of the methyl cation CH3". explain using VSEPR {l sentence!} Shape: Explanation; Ht 5f” hybklflllit’fli Ignored-1E 1hr: ertt' t’_ dfi+‘-5I"!'-" fur-yfithtti-fi It“ -|'o n-e more {c} How many stereoisomers are possible for menthol? Answer: if; B [see structure below} {d} Draw the two chair conformations of menthol lpeppermintoil} and circle the most stable. Note: show art artist and equatoriai bonds corresponding to those on the structure below. H CH3 H H31: CH3 Mehth oi M ' "'~- ~.._ {a} How many optically actwe stereoisomers are obtained by monobromination of pentene CSHW’? Draw a clear stereochemioel representation of each stereoisomer using the template below as a model Do not write the same structure twice! . - . . - . 2 “I'M-H “vi-L12"- r2: 1 l1} '.'Fr:l1 Iv“- l- - I ILL-l.” |.- .l -_||'-I'.._JIN {HELHEIHE l-Put filmy 5;? [MIJI- it: (11%;.fo VHF;- trJ :rt-l" (ti-T -5!_ fit 14. 2002 J. Frechet. Berkeley Chem. 33%. 21302 Midterm Exam #1 _ Page 5 of it} 4. t 12 points] {a} Removal of two protons from propyne HCECFCHg leads to the propyne dianion [CCCH2 12'. Write Lewis—dot structures for two resonance forms of the propyne dianton in which a” three carbon atoms have an octet. Do not forget to show the location of any charges! Circle the most important resonance form and explain why it is the most important. came-rt 'nF 3 “-' 4' " "‘- 5 air-:1 A _ =3 It. a a} «hat: meager. are" hu-‘T'Tr‘FL .‘ilfi'fi'iilnuiFJ :I'rTIDE? Emnlf) - jtll rttdarfi have a gee'nrp ULIE‘T. to] Calculate the change in free energy {expressed in Keel mole") needed to change the equilibrium constant of a reaction that takes place at 27W: from t to mt}? Show the equationts} you use and the detail of your work. are ear lie Ken-r T= Ear-*er 12 - 2 patrdF-flrr-o'i --Af'.'it£T Fete a t-E true- i art—- o retreat J H “t f t“: M“ 1 teen} tote-tit : — 2111;: ‘F‘f'j'j'll‘ffi‘a‘. --:_~Tle Ian-ME yin-at: fii’mfl. ITWI .- _-}l:; I; It; refit lief-12:1 Answer: : 2,-4 t. 1.: mt ymoi I] a ass: .1. Frec'net. Berkeley Chem. 3A EDDZ Midterm Exam #1 Page B of 1D 5. l 13 points). (a) Name the scientist who discovered that the plane of polarization of plane polarized light is rotated when the light is passed through a solution of camphor to] Name the scientist who discovered and quantified the dependence of reaction rates on temperature. _ .7:- if,”- K- i-iH'I'l. {c} Write the Lewis—dot structure for the sulfate anion 8042' in which each oxygen is bound to sulfur in an equivalent manner and indicate the formal charge {if any} assigned to each atom. Fru- Eritfi '1 I'J'l-‘o' .7.‘ I. g... :--_'-l if: {d} Consider the equilibrium: HA + H20 A' + H3+D Determine the concentration of [HfD]. [PE]. and undissociated acid [HA] for a 1M solution of acid having pi“:a = -2. Show the details of your work. 'rfetg[‘.--I.=-'="_L= two _ a tug.- [fl_1[Héfi‘] it’d: it}; |“é‘$FF‘;.:lJF la" in r [M rig-vi: i1 {HID-HM} _._.— . _ 1 “'41 W lift—fl .. is 55.“:- 2 , I-FH “flit-112.1: Farm «.1... , it) we 'tftifrt‘2361 p : :t’Jr lU'fil 1 “WU 51-”- ' 1’5 [‘e’LI’rflC : —iuu: E|mT--flr[-Iflnl'} a-I'LILEIi : FWD: "m-“fi 2“” Z 2 .1 .L‘tf’lt-“l [a]- {reset [Hal= enrol I Answers; [Hffl] = u Chem. 3A ZDUE Midterm Exam #1 Page T of it} is) 2002 J. Frechel. Berkeley 3413 Paints} {a} circle the functional groups in the molecule below and name them 3, WWW?“ are”? lo’nexane [show all onforrnation of cis-l—ethynyI-2-methylcyc an the ether chair {ti} Draw the more stable chair c d explain why this chair is more stable th pended atoms on Ct and C2} an conformation. LELl-l ECH _ 1 E H .—L :{H (“a l 'l-‘r “T _ ._ ll :5 races 51mg}; Minus: LEWW “'5 Naif? n‘plé'ullf‘y '5 lI‘I I‘qUEI‘TDFIRI f-‘Dfiiflflflran‘d m5 Hp: pp Ifildd-uwal intexriltlflfii Hectic acid has a specific rotation loll” = +1335“ {cl A sample containing both enantiomers c at is the percentage of Given that the specific rotation of PURE [-l—lactic acid is [ckI = -3.B“. wh {-i—Iactic acid contained in this sample? Explain and show your detailed work. 2;].0 voted? = i'll =35“ fl.k-.' \ I_ a: ‘ —'-—-—yign.1_—_ 1% n l+ ; lull n L)”, _3_%D 15% IS Fulfil H} 5450’s [—1 zoom. Freche1.Eterke|e5r Chem. 3A EDGE Midterm Exam #1 Page 5 of to T- i 13 F'D'IME} {a} Consider the two chair conformations of the 1,2.4—trimethylcyclohexane shown below. Name and tally the strains present in each conformation. calculate the total amount of strain in each and circle the most stable chair. Answer: Total strain = Leia: sell lmol Answer: Total strain = 3.1 l-crn.l ln-o‘l {bl Match the letters of the staggered and eclipsed Newman projections below to the indicated positions on the diagram describing the relative energies of different conformations of 2—mothylbbtene. cha HECCHE. A H H B ' Hie H H H u H CH3 ch H H3314 c D fl H H CH3 H CH CH3 H31: 3 Staggered Eclipsed conformations conformations Du Baa man “age 24g“ and“ 35h“ Angle of rotation —-+ to zooz J. Frechet, Berkeley IChern. 3A EDGE Midterm Exam #1 Page 9 of if: 8- l 1'3 points?) {a} The free radical chlorination of alkanes with sulfuryl chloride clsogot does not produce the same mixture of monochlorinated products as would he obtained using Clg and light. Using the product compositions below. calculate the selectivity,r of the ‘SDECl radical for primary. and secondary.r hydrogens. Show the details of your work. ’_,_---,£‘I. __H_ CHacHQCHQCHECHECi {23%} FE. _-"“-. - - fin. ‘- GISOECI ZCH3pH3§H3CHj~CH3J *—h—"’ CHBCHGICHQCHECHEI {48%} E5 ..__,..' '—’ '--.1_,--"---' '~-_--- 1.- {‘3’ CHacHECHCICHECHg {24%} c wallet?» selerflw‘r‘}! it fig ‘n' I” 1 a sis] : 0,13 E‘ 2" g 4: Lls‘rflrifl't 1‘13 L :r. i 4: L "' e'r'tl HJ‘iF ET’I'q'y'i'l-i :' - [114.43 *2? :11... r" 3'5}! ' “'c . is it '; fl:d.1& .— 15,14: W Lia-Aji'li 21': fl-E'qw Z: D-I'P w ._ :Ilr'r’t, - Hr: '.! HS'X: TIL '1 _ q‘ gxzujfiw H— “E’DW J_£_gB—'.q£ gin-ggllg Yfiilg. 4);: fllq-LEI‘N - :2 flail xv' Answer. Relative reactivityr secondaryiprimary = {b} Consider the chlorination of alkanes with chlorine in the presence of light. [i1rfillkane A {GEHHJ reacts to produce only one monochlorinated product. Write the IUPAC name of the monochiorinated product. E. 1*.th H; r.-' !-i1__._fii—i7lf a; E'_' ' Answer: I s—‘r L: Jr ‘3- —“" '.L ‘— ‘ «t :9 id {ii}. Alkane B {CTHW} reacts to produce seven monoohlorinated products {ignore stereoison‘lers}. Write the structure of alltane B. l—rhlueflpenmne I.I 1 II I. I 1 1 tin-Csll-Lai-gfl—LsL—H I I 1 l 1 l i 14 H H H 'H- 1 H Answer: 2oo2 .i. Frccitct. Berkeley Chem. 3A 2992 Midterm Exam #1 Page it) of it) Note: There are no questions to be answered on this page. it only contains data that may he of use in solving the questions contained in this exam. got all of the data gigen is neegeg; Value of gas constant: R = 2.9 cal rleg‘1 rnol" Value of absolute zero {keluinj = —E?3°C Value of a {base for natural logarithms} e = 2.?19 Bond dissociation energieslin kcalmole'1}: HGHEeH as; RECH—H 95'. R3C~H Ell; Cl—Cl 59: Elr—Elr 4E3; I—I 3E: H—CI “33'. H—Br BB: H—l 'i'“l: RCHl—CI Bl: RCHE—Br as; ecnget 53-. ech—ct so; RECH—Br as: ego—ct rs; egcwar cs: ‘u‘aiues of strain enargi_e§_: Each CH3 ~ H eclipsing interaction: 1.5 kcal rnol'1 Each H v H ecliosing interaction: 1J2} I-tcal n'tol'1 Each CH3 — CH3r eclipsing interaction: 2.5 itcal rncl'l= Each CH3 — CH3 gauche interaction: {LEI kcal rnol'1 Each t-Eluttrl r CH3 gauche interaction: 2.9 kcal n’tol'1 Each CH3 — H 1.3—oiaxial interaction: [1.3 ltcal rncl'1 Each CI c H 1.3—diaxlal interaction: i125 kcal rnoi': Each CH3 - CH3 1.3—diaxial interaction: 1.6 lccal rnol'1 Each H - cu 1.3‘cliaxial interaction :c_1 I-tcal mcr1 Each H - crcHgg 1.3—diaxial interaction: 2.5 kcal mcr1 Formulae used in solving quadratic equations: ax?“ + h): + c = D it = [-h 1 {square root or {o3 — =1 acl] l 2a Partial periodic table of the elements. 6 . 15.9994 19.9999 99.1?91' l3 1% 39.9?39 32.999 3 34 22.9999 H9959 ‘l 29 K Ca 39.9993 £9919 1 A_ St 239555 2 3 3 Ga Ga As Se 99.123 T191 H.92l5 F996 31 Na '9 ...
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Chemistry 3A - Spring 2002 - Frechet - Midterm 1 -...

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