che275_exam1_ans

che275_exam1_ans - xii/MSW" fl flw’wS/Q CHE. 2115...

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Unformatted text preview: xii/MSW" fl flw’wS/Q CHE. 2115 FALL 21111116 print name sign name last four digits of your ID. number FIRST HOUR EXAMINATION All answers should be written on the exam. Cleorbr indicate your answers in the spaces provided; if we have to guess as to what or where your answer is, it‘s wrong. Where applicable, outline the logic or mystical principle you used to arrive at your answer, as partial credit may be awarded for correct approaches. 1|Work pages are provided at the end of the exam; if you need more ask. Make sure your name is on each page of the examination. Advice: This exam is long given the time allotted, and you are strongly advised to read it through completely before you begin. Please respect those around you taking the exam and refrain from groaning, sobbing, bloating, shuttling, rustling, singing or ranting. Quiet motivational growling and Vigorous model popping are permitted and encouraged. A data page is provided as the last page of this exam. {1] 12 pts ........................... .. {2) I 1 pts ........................... .. (3) 12 pts ........................... .. [4} 15 pts ........................... .. (5:. 15 pts. .......................... .. (a) 12 pts ........................... .. {T} 12 pts ........................... .. {3] 1131 pts ........................... .. Bonus 1 pt ............................... .. TOTAL [lull-[1 pts} ............... .. Bonus point for showing up to lecture on time {or at all). Prof K keeps his top secret poker notes in . ( 1 pt}. heated Pr film?“ I. 1iJt'ho would have thought you would find these gems on an Organic «Chemistryr exam? There must he a catch, right“? There is. Incorrect answers will negate correct responses. Consider your answers carefully. [12 pts} {In} Rank the following compounds in order of increasing heat of combustion: A. B. C. D. "l Q1. Ear-auc Clo; T- ? en'lft W C A g D S I“ 2‘? lowest dHc ----------------------- "1* highest dHc (h) Ran}: the following in order of increasing Bronstcd acidity: (A) HF (E) H10 {C} CH. (D) NH; C; ‘D 85 R least acidic ----:* most acidic {c} Rank the following elements in order of increasing electronegativity: {A} 0 (3} C {C} F {D} K least electronegative ———} most elecu'onegative (d) Rank the following compounds in order of decreasing heat of formation: {A} [3} {C} {D} ‘0'" (Er U Eflig highest dHf an} lowest on page 2 of 9 2 (a) Draw Lewis clot structures for each of the following compounds. Show all bonding and non-bonding electrons and calculate the formal charge on any,r charged atoms. Elements shown in hold-face are central atoms to which all other main group elements are attached. [11 pts} 9 gay {a}CH2C12,dichloromsflta-ne K ‘ rail 1 H __, (are H —[ C231 QacQ.‘ écu DMstsk-wa Jo {a} CH3CN, acotonitrile Us ’l H - (TL-h CE N: H {o} H1302", formate anion :3 H u. “"1 Q. W1551H6x “ac—“h. J r..--—-—._ H o: ‘33 61. his to} croft“: c.31— [dll [CH3]250, dimethyl sulfoxide E) H t :16) H l ‘21 H~—r:.*—S-——C.-L' 'l a 'u H H page 3 of 9 Lfiuflfi 3. (a) Supply bond-lino otruotu: of the organic compounds which corrosPond to the following IUPAC designations. [6 pts) {i} 3—mhy1hex one (ii) cis- ] -hutyI-3—mefl1yloyolopentane [iii] 4—(1 '—methyipropyl]ootano {‘13) Provide IUPAC names for the following compounds. [6 pts] {i} {CH3 )EC HCHECH(CH3}2 (ii) m” 'fi'musv- 'r- (13ch HEEL.“ a C‘tflLongmL 6?... "Home; -- ‘4- M‘WMJ HK-leo ngthoto («am—Le ophnvfi paged ofEI Eh Ma.- 4. Indicate whether the following pairs efeempmmds are {C} cenefimfienal [smetmaljl isomers, {R} resonance forms, {S} etereeisemers, {I} identical [a eategnqr the: includes conformers] or [N] none of the above. {15pm} and Wm/ L U 03} S and (C) H—-é——NEEN: wfi C==N==": "" {d} {e} 8 CI Cl Cl H CH3 H’ CH3 “m H EH H GHa Cl 3 EKRLAJY a? Lef‘mxol} g Slack page S at" 9 ?M'rTf0" e 5. (a) Sketch the potential energyr relationship corresponding to a‘fbl 360° rotation around the C2-C3 bond of 2-methylhutane. *Clearljtr indicate the relative energies of stable conformations {energyr minime} and transition points [energyr maxima}. Hint: A time-efficient way to approach this problem is to do parts {a} and {b} together. (5 pts} lain“ _—-,__-— E 4313/ 1/ L _ In T316 KL}. _ ,. _ _F , _ __ a" I m [P S ‘e. I] fill I21] 130 140 film 361'} I \‘ degrees rotation {h} Draw Newman projeetions fo eaeh of the eonfo'rmations of Z—m ylbutane whie eorrespontl to an energy maximum and mininito'o on the potential eun'e from pa (a). «Clearlyr ind ate the points on the curve withwliioh eaeh proj'ootion is associated. (5 pts) I‘LHM t hflg H Ewe La ‘m. M H MeH NH HMH/ N‘Hh/ M?" W H n H rt . . :1- rte-H 1mm [m‘m-i—ed- a. w, {nu-we ELL 5 ale 5 ie- 1-3? _ 1 {4-14 ed 4 i H-l’r eel-{m {e} Estimate the energfiilpit'fereficgs between the maximum and minimum energy eonfon'nations of 2-mefliylbutane. Indiealelhese's'alues on the potential eon-re you drew above for part (a) of this problem. {3 pts} _ z? I W C}; gar” UCJ gt- page a of? (Prat-.4; J Lflu M )2“. MM £14 6. Draw all cf the iscrneric, cyclic hydrccarbcns having the molecular formula CSHm. Be aware that duplicate structures will illicit some hideous form of punishment. {12 pts} page T of? ’1'. Each of the atereeieemerie eyelehexanes A and B exists as an equilibrati g mixtm'e of chair eenfemmfiens. i?" {a} Draw the Possible chair eenfennationa ef isemecrs A and E. Fet eaeh isomer clearlyr indicate which chair Gal-(mil. TL TL (b) Based on your analysis efehair eenfennatiens in Part (a), which of the two iaemeta do you expect to have the lowest heat effennatinn‘? Estimate the difference in fiHf between A and fl. {4 pts} 1’ . ‘v. page 8 ef‘E}I Krista: as”! its 75%} Not too bad? Excellent. Check your answers, then give this one a shot.... 8. The hydrocarbon [4.4.l}]-bicyclodecane {commonly refetred to as "decalin"} exists as two stereoisomers: tronsdecaiin and cis-decalin. decalin WRHS-dflfifilll‘l cf5,dflcalin {[4.4.fl]—bicyclodecane) {a} Which of the two isomeric decalins is more stable? To prove to me that you didn't just guess, support your answer by estimating the diffence in energy between the ctr and trans decalin isomers shown above. Hint; try thinking of each decaiin as substituted cyclohesane. (5 pts) +2 :3 am SIS—5% la, 315638 £1.30: (HAD {-3 {b} The conformational properties of the decalins are interesting. Trans decaiins are conforrnationally "locked", meaning that the individual cyclohexane rings of these isomers are physically unable to perform the ring inversion that we normally associate with 6-membered rings. Make a model if you don't believe that statement... but wait until after the exam. Right now, we have other fish to fry. in contrast to the trans isomers, cis decalins are capable of undergoing a coupled ting flip, in which not}: of the six membered rings undergo a simultaneous inversion. An example of this "double flip" is the cis dimcthyldecalin system shown below, which exists as a pair of equilibratng conformers C and D: are f1: East—ace Qla CH3 CH3 butld' Jr"... W H30 _..——"‘ C I CH3 D qa. UCD‘L Estimate the energy difference between C and I) and identify the most stable conformer in this pair. The hint from part (a) is usefiti here, too. [5 pts} +1 fi 9 15 tom 8 W lo, 32: hymns j“ as . 43 ...
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This note was uploaded on 05/18/2008 for the course CHE 273 taught by Professor Kallmerten during the Spring '08 term at Syracuse.

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che275_exam1_ans - xii/MSW" fl flw’wS/Q CHE. 2115...

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