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# exam 2 key - Chem 2210 Organic I Exam II — — 9:05-9:55...

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Unformatted text preview: Chem 2210 Organic I Exam II — 02/01/08 — 9:05-9:55 a.m. Name: This Exam Has 14 Pages Total Pages 13—1 4 are scratch paper l.(3 pts) Draw a Newman Proj eet of Butane with the following torsion angles. 600 180° Jr\ ‘H 2. (2 pts) Draw a Newman project for the two types of transition states that lie between the two types of butane conformers. The following graph is the potential energy diagram for butane. Potential Energy kJ/Mol 3 kJ/mol 14 kJ/mol t y Torsion angle in degrees 3. (3pts) From the graph answer the following: *3 Gauche Anti AO‘ ism/mi 4. (6pts) Calculate the ratio of gauche and anti conformers expected at 298 K? Show the equation you use to arrive at the value (see'the last page of the exam for helpful information) and show the equilibrium and which direct it lies toward. “bk/QT 4'\ Que median [3 (‘9 = - (2.“? Qn‘eaao‘ \ﬂaq z: a, ﬁQ-{F’rbﬁi , . . x : g1 ' 2a: u was op Quack-m. —.~ awn S a. {U a h \1 "'1‘2: _ _ ,h' In} t WW.--” r“. .3) Fr“ _[ d! __L . ALI: 32;. W" .\ c ‘7‘.; ‘ , k -— a q ‘ ‘ 2T“ [Us ‘Leq a C’— - s2 up») . Id: I?“ “=— +\ con-QC? éWQC’noo CW: 2&- 4: ‘5 cam-:23: mama.- 5. (2pts) When measured in solution the percent gauche and anti for butane is 44% and 56% respectively. Provide an explanation as to why this ratio differs from your calculated value? *7- “?mam are "(Loch C304.» cats 2 \rt'xﬁt't ‘51?“ ‘53"! “‘3 .. . c K c. '- -v—“ ' an .. ., . . - ,, ..: .. r at: v, mien. . Les a cash: a); 2“: x , 200 7‘“- ‘ ‘ ‘ ‘" :‘ \ _, ., r- "r A . ‘ (Sid " t» e F '4’" .5 Uk .1 "-‘1' -e'("-.;,. :1“. L. . '- 3’» 'r- ‘w; ‘ k ‘ *1 55 . "fir- - 14"":\ ‘ r“ (q \r“ '\ J : \ "‘ ’ \ 3 t \ 6. (6pts) Convert 3—Fluoro—4—i0do—4,5—dimethylhexane into a Newman projection looking from carbon three to carbon 4 and then determine which conformer is most stable about the 3—4 bond. *3 vii-or proper 4:7. an»ka y N Q “a” m :1: r -. i 9: - £33 " ‘1'! 4% 3.”- H ,, ﬂ \ ﬁsv 2 I" t f A 5‘ Rita—E;- J “Jr 9;: \_\ t (l Cori-(Q5— F; Ac "1 ﬁHtJOUZ. 7. (4pts) From the following Newman projection create a simple line drawing with hashes and wedges to illustrate the groups that reside behind and in front of the paper, respectively. BF \ | -. 5: HO Cl , UL- L \ 1-; a .. D 7 n 2:!" ‘ \r.- i m \\_:g ‘I‘ ‘ I } .1 77‘s “W. Uinw K‘ V ﬁrth, H } Me r . m" f r \$- tBu i 8. (lOpts) a. Draw the ring ﬂip for ciS—I,3—dimcthylcyclohexanc with the most stable conformer Z drawn on the right—hand side of the equilibrium arrows. 1 :6 __l 3‘ '1' ~\ gov a- \ 40* 9”?” CorfGC-‘r Sq. Arm»an 7,- b. Calculate the equilibrium ratio for cis—1,3—dimethylcyclohexane (AGO: —45 kJ/mol). A (b a M QV"‘\\\LCC\ Llama”! K‘s-SHHLZR‘E“) \‘Kc Q 1 mamas it #1 a; 63:. if} («or was: >1 i "imiaaqaxsa 4: 1 ‘Aaa 3t\ 2 c. Draw the ring ﬂip for methyl cyclohexane again with the most stable form on the right. What is the ratio for the two conformers? ‘. J‘.\ +\ ,. l_\‘ d. From the data in b and the data in C estimate the energy of a methyl—methyl interacts that is 1,3 across a cyclohexane ring (should be larger than a methyl-proton interaction). H e“ 7mm; m a. M a b" V“? 1" m n z .‘ {\M EN“: 2 3 H ‘ + _‘ Him“,- i “"—.,._‘_“.,e'";3 " l f ’ F . . A\Q;3.<\(\\ :2. \fq \rr‘rl frwicﬁ " m \‘5 N In; _ 1 £565? ‘5‘4 "11‘ “Man 1' ' ‘ It i”? I ._ .-_ n; r.. w r r“; 47%“ \. w-i I} I "' v A‘- L) - -- I-li ‘. «aux C. \$ é : \O .175 \C CraiK any-CH3: \inii " ‘r “Jr 3 '3‘"- * “(d/u 9. (2pts) Draw the most and least stable conformations of pentane. Most Least 10. (Zpts) Draw the cycloalkane that has a ﬂat conformation and the one with an envelope conformation. ﬂ; Enveloge -\-\ 11. (2pts) Draw a bieyclic and tricyclie molecule. Bicyclic Trioyclie 12. (Zpts) Draw a primary, secondary, and tertiary carbocation in order from least to most Stable. ‘ C" a, . H "., I its“ a (")1 ’c 1. u 4- r» r w u. c. a .r . . '. ' ' II ‘I‘ l .I 9925 <’ r 4‘) ‘3 g ‘* ’ 00* | _ , w- J L» , m5 0. u “r \x " in f ‘“ ﬂ . ms n a v | u r ‘ c” a 9- w a ’na ‘0 WM \ roe-N "1“ I la Mes-3A '19: akiﬂ 13. (lOpts) Benzylic and 311in cations are Show below. These cations are as stable as tertiary carbocations. Use resonance structures (3 for the benzylic case and 1 for the allin case) to illustrate why this is the case. '91 't—i o l j) t}; a It A '1 in» 1‘ q: '1. ’I A. J.» H E. l; 9‘". and? ":3? has ‘“’ ‘6 “" ﬂ. 6"“)? a}. w) in...“ f 1‘: @h‘ —I—.._‘-‘ «3—) L; {,3 .y k 2- 2- "f‘ ‘2. Benzylic carbocation H ‘49 Ar 7. "\ I r 4-9.5 (9 1L ..- H / - - —.-. a) H allylic carbocation l4.(4pts) Draw propane, ﬂuoroethane, and ethanol and explain why their bps are —42, —32, and 78°C, respectively. What forces contribute to the observed physical prOperties. "EQov can .M" _ if; mg mmﬂ‘ﬂc\ _.\ ‘, , _ yin-ochre \ mun-imm- "r u :. ~ 8 i \ -,. . , w t ‘7‘ ~ » ...a __ . W, V. ‘ X H _, '6 =1 \‘e t t “a 7-“ w -- r'“ 13““ a _ tee-air:- i‘ess \« xii-(Ti? 1'5»- ‘ - \ANémC gm jxxﬁmc‘l FR, 1 “\$3555”. "- "1' V’FDSA“ A? 7- Ar?— 6 l7: (Ki: “V 7 Shaw“ ﬂw7x 16. (opts) Draw the following oxirane r— acetonitrile — propylamine +\ +\ o m» e H. z — Adipic acid Acetic anhydride — lsobutyl acetate +\ ILL: a": “'r ca ﬁrm“: . ‘ WOC) a; 4) r l7. (6 pts) Draw a reaction coordinate diagram (potential energy vs. reaction coordinate) the following situations. Label any intermediates. The TS Resembles Reactants The TS Resembles Products An SN] reaction "idyv. 563:“Qcit. g}. P “H 4-1. “GA/v. Los— 18. (9pts) Provide an arrow pushing mechanism for the following reaction. Make sure to identify the initiation and prOpagation steps. Also, draw one possible termination pathway. QCHS Bra, Light CH3 Br ‘2 " "x. 03‘” ‘ - r~~ . r CLan «W ‘Pﬂm A. i /" wows ﬂu; 7} V ‘ 5,?ggxpé NW,» C w ‘2 “aﬁmfgkﬁ f e L: Pam o my) -\ ma ,. W w 5 ‘5“1 1' ‘: 4"“)- \ I‘ l ’ ¢ 1 \N ‘ a; < C' \J Q7 .i >— —: ‘Ww {Ina 4 “Yea V‘i‘Tt maﬁ- ec’, m 1 2m. -' ,4 a? tit-1c M- r. if " M x1 ‘ “ u M» i J 19. (9 pts) Using Bond Dissociation Energies (BDEs) calculate which of the two products is more favorable. BDEs are featured in a table in the back of the exam. To perform the calculations, you are required to pick the fragments from the BDE table that most closely resemble the starting materials. Show the fragments in a simpliﬁed equation like I did in class. Only credit will be given to answers showing work and provide a calculated BDE. H ,2‘”:“""“H“ + 2. Gear H ‘ cpccegk H 4' Chaim ME Bra, Li ht Me Me u g ‘ + H H H H H ' H H H 4-7. cowéck Ranginer w, .\ i u. ‘ V‘ F 5 i\ K» ’ : 3‘} 6:!“ _ gaunt-n- » V‘s-q, .- - —*s€, } _m [IA—u 1. (.3. m Sir {me i “ (a w "4’10le r— w \L\ VHS (Amid 4r \ \- 7. cox-Md: mew-inst“ €75.211k“t d g i I if! fie“ t \V a 1W __ :— v l r“”'"“' ‘ “ we-.-) ‘ = r: «i ﬂ _ N __ W {EMS v : M‘ “w ';.".;'< w "3 M dime \T'L ‘ m 'L\\ LiF'RQ-Efga‘: 3.? * atria“ cm“ H ro Cot-wed: HM“ b1 (swag Gnome ‘02:;qu euc— mcocnedc o (foamed: dan 20. (l 2 pts) Based on the following reaction answer the following questions: a. For the reaction above circle the new carbon—carbon bond that is formed. _ b. Identify the nucleophile and electrophile by placing Nuc and Elect in the boxes provided above. c. The lower the pKa of a leaving group’s conjugate acid the better a leaving group it is. For the above reaction two potential leaving groups exist (the bromide and the carboxylate). What are the pKa of bromide’s conjugate acid and the pKa of the carboxylate’s conjugate acid? 1:.) a, '- \\ \A' Kim /“~<"\'\a ?\ch: “‘5 gage»: 4r 9. +7. d. For the above reaction rate = 1<[ “o” ' ]. Based on this information and other knowledge gain during this exam predict the transition state structure for the rate determining step and identify what type of mechanism this reaction follows. +'-\ 10 ...
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