Answer Key 2008 Midterm #1

Answer Key 2008 Midterm #1 - M C. F. Bernasconi Chemistry...

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Unformatted text preview: M C. F. Bernasconi Chemistry 108A Winter 2008 First Midterm Exam — February 5, 2008 This exam consists of ten (10) questions for a total of 100 points. Try to answer all questions. Write your answers in a Blue Book. Put your name and your TA’s name on the front page of the Blue Book. 1. (16 points) Some of the species shown below represent a resonance structure. Identify those species and draw as many alternate resonance structures as possible; using curved arrows show how the different resonance structures can be interconverted into each other. (a) C1—CH2—CH=CH—CH=CH—@* ID I {1 Q-CHr—C\4=CH-‘—’Cu~ Guam. U i‘ CH:sz EH - cu z (ll/CH = CH: (‘H's‘Cl‘L’Cl‘l’Ov no/ 0x FestjMQV'CP StZYkC‘MrL fl ,0 o‘ (c) CH3—CH\—-/-C\/\-§ 6’» CH3, 0“ : C< H l/K CH CH d ' . a ( ) c (7 CH é—-—> Km/\C é-> / \C * H ch. rt. <7; 2. (9 points) Give IUPAC names to the following compounds. Be sure to include E/Z terminology where appropriate. CH3 (a) 2 __ e 44¢ _ A‘me WQoga/wpéane CH3 (b) [>CH2CH2CH3 /— (:7 ego/3n? %flropan€ H3 CHCH CH ' (c) H\c=c: 2 3 (2 HMO, firm/£74 l-hwene CH3/ Br ' ' 3. (10 points) Which of the following compounds are bases, Br¢nsted—Lowry acids, Lewis acids, or neither? CH3 CH3 CH3 _ + (a) (b) CH3O (c) CH3CH20H2 CH3 CH3 baSC BY omit/f “Lwa aux CH3 Dagger (d) Mg2+ (e) (CH3CH2)3N Z ems a o: km 4. (9 points) Which of the following neutral molecules have formal charges on some of their atoms? Show the charges. 4’- 69 /OH Q/OH (a) H3B—PH3 (b) CH3CH=C\ (c) CH3CH=N\ H ()9 ho Charges (6 points) Add curved arrows to the following reactions to indicate the flow of electrons in each. 0. 2 v ,o (a) H3C—#—/C‘1/ ———> H3C-C\/ + Cl— OCH3 OCHs /~1\/‘\ 1: (b) H— IJH + C1. ——-> H_|° + H_C1 H H d B show the two chair conformations of trans-1-tert—butyl-3-methylcy- 6. (8 points) A an more stable? Explain your answer in some detail. clohexane. Which conformation is (CH3)3 CH3 chmb I CH3 A B H .9“; cg“); 0“ & 5/(on5 /. 3 «dl'aw‘a/ Ih/AA MAJ/“s W“ .V gig? fink/o Silvana/5 fies/aé'fl'y A V\ w m oar/WM Wm “cm, H (“we (/6 A MHZ Qmagér Max “5 ill? ((Vnggc 6ruA/4 .' ,‘3 figs S/wr‘vsé Mame/mt A, mm 5;; more 3566» {flak (8 points) Consider the following acid-base equilibrium between phenol and the nitromethane anion: H _ + ’O— _——> O The pKa of phenol is 10.0, the pKa of CH3N02 is 11.0. (a) (b) (a) [5) Which side of the equilibrium is favored? How large is he equilibrium constant K for this equilibrium? 7}“ €174 is ‘fAuovel/ k : KAPA‘CV‘X ’ /O-’0 I KAN/3 RIO/L low” - (16 points) Consider the following reaction: (a) (b) (0) CH2 CH3 (T —» Ora Show the mechanism; include curved arrows to indicate the flow of electrons. Draw a free energy versus reaction coordinate diagram; identify AGi, AGIt , AG? , Avaera“ , and AGivemn on the diagram. Assume that the first step is rate limiting. Explain why the reaction does not lead to the formation of O/CHZCI IN m (48/ $473» 71445 CAAN is final xéyn AM “we fie évé‘avg (AYKOQAVL: SAW WAN M, A€MCP Canno/ CUM/364 a? (4144?. 9. (6 points) Which alkene is more stable? (3) CH3CH=CHCH3(trans) 0r CH3CH2CH=CH2 Explain your answers. (60 (rm/=(HC‘Hs / m) i: MM saw/é W“ (“SCHZCVJ‘h mamé flame ’g7/ijCODjIAj4/4'Gf [Alerac/st 40% M me/éa/ 3W5 Mgng Con/mg m/fi CHSGFLCIRC‘N; —‘ W m ,‘s Afloeramjolqéyémi oné m/K one 452/ 3’07" mummy {Ac/5r: (rgturr/M‘t/J fin Au 6/3— 5,32 AWL) M‘é [7&[7/1fl!=(wz 0%? {M W- 37“? 3053?} Awh We SAWW Maw 5,9459 5mm) (HgflfsfHfi/z i; mm? , 71? as MAN)? is Wj/aflr‘gflei/ 374”? CYOIJJ’l‘f-J‘ “£390 4/” {MI/'3 Homer f§ r’YMYP 3(Ag6- 10; (12 points) Each of the following carbocations can rearrange to a more stable ion. Propose structures for the rearranged cations and show by arrow pushing how the rearrangement would occur. CH3 (a) CH3CH2CHZCH: (b) CH3<l2H6HCH3 (c) CH; CH3 (PW “9 ~+— \— CH2 fl CH3 [Hi‘€_ CH3 (Edele H H '0 (“Luna ‘10 Ct»!le {mo‘e 39% ) V i .r a (“3" . “UV”: 3 CH7; c— («z—cu; [Mamie sum CH7) CH3 2° 2° CREE“. (moi? SéIAM’) CH3 + CH j“ /l new slim A, I > \ /O %0(AAO¢\ [Move \ a.) ...
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Answer Key 2008 Midterm #1 - M C. F. Bernasconi Chemistry...

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