Exam 2 key - Chemistry 333 Exam 2 Oct. 12nd, 2010 CHEM 333...

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Unformatted text preview: Chemistry 333 Exam 2 Oct. 12nd, 2010 CHEM 333 Fall 2010 Exam 2 October 12, 2010 NAME: REClTATlON DAY: 1. Be sure your exam has 10 pages, including this page and a periodic table. 2. Read the directions carefully for each problem. 3. Write CLEARLY; illegible answers will be considered incorrect. On questions requiring derivations or calculations, show your work in a manner that can be easily understood. 4. Avoid even casual glances at other students’ exams. 5. Do not use red ink. 6. Stop writing and hand in your exam promptly when instructed. Late exams may have points deducted. Please leave quietly if you leave early. 7. Put away all cellphones, pagers, notes, books, etc. You are only allowed a writing implement and molecular models. 8. Work the easiest problems first. Question 1 12 points Question 2 ' 18 points Question 3 16 points Question 4 22 points Question 5 14 points Question 6 6 points Question 7 12 points Total 100 points Bonus 10 points Score: 110 points Chemistry 333 Exam 2 Oct. 12‘“, 2010 1. Multiple Choice —— put the appropriate letter in the box 2 pts each (12 pts). a.) What is the total number of stereoisomers possible for 1,3-dichlorocyclopentane? a. 4 b5 0.6 d.7 b.) Which of the following statements is true? a. All mirror images are enantiomers b. All molecules that have stereocenter centers are chiral c. Isomers that are not superposable on their mirror images are enantiomers d. Superposable structural isomers are enantiomers The most stable conformation for 1,2—ethanediol (ethylene glycol) is shown below. It is the most stable conformation because: H H OH H OH H a. this corresponds to an anti conformation b. in general, gauche conformations possess the minimum energy. 0. it is stabilized by intramolecular hydrogen bonding d. it is an eclipsed conformation (1.) Which of the following cycloalkanes has the most ring strain? a. cyclohexane b. cyclobutane c. cycloheptane d. cyclopentane What is the least stable conformation of cyclohexane? a. Chair b. Half Chair 0. Boat (1. Twist boat f.) In order to reduce the energy of cyclobutane, one strain increases in order to decrease another. Which ones are these? a. Steric increases in order to decrease torsional b. Steric increases in order to decrease angle c. Angle increases in order to decrease torsional d. Torsional increases in order to decrease angle can? Chemistry 333 Exam 2 Oct. 12nd, 2010 2. Complete each of the following sections below. (18 pts) a.) ( Label each chiral center (stereocenter) with R or S. Draw the enantiomers of the compounds. i") a“ E ~ am y -- i ,,,, ,_ I- / / l” \ k f"; x) l //\[< i N x a“ 1% f E a“ WAN.“ N» T «TV, > ii { OH OH OH OH Chemistry 333 Exam 2 Oct. 12“, 2010 2. Complete each of the following sections below. (18 pts) a.) ( Label each chiral center (stereocenter) with R or S. Draw the enantioEers of the compounds. t i l a l . 5 2‘3 , ,5 A“; r l 4 CH3 1 1 if it}. E g x - u I ywtmaa, r; / If” V V I t ' l / / ‘ ‘ i i a t aw»; bl’ ‘ ) "‘ K «1:1: ll: OH X'fo M22 \(ifi ‘‘‘‘‘‘‘‘‘‘‘‘ dz C} f/“xk I’M/"“wwfihm “if; OH r mm Chemistry 333 Exam 2 Oct. 12“, 2010 3. Follow the instructions for each section below. (16 pts) ' . A N, 49;- a.) Circle the two diastereomers. N we? r 4 m“ 4;, MM 33ngme HO \ m A (a? ‘ é 0H be) Circle the two enantiomers. c.) Circle the two that are the same structure. View 3‘ {WWJ flBrz OH f C," ME” t“ v War Xi 4“ w, ,,._;,,,W,.,..y"“ d.). Circle the one that is a constitutional isomer of all the other structures. ‘i , ‘ CHO CHO , H OH H OH {t1 H:i:OH Ho OH h H CHZOH CHO f.) Circle the compound that will have the lower boiling point. (/1 butane l-propanol Xi‘an Mafia/J g.) Circle the compound that will have the higher boiling point. (“pentane 2-methylbutane f . r" h.) What force causes the compound in (t) to have the higher boiling point? Chemistry 333 Exam2 v Oct. 12“, 2010 3. Follow the instructions for each section below. (16 pts) a.) Circle the two enantiomers. f on... HO : it ~ m, M,_ t. x «.61.. x?“ I? 'd ‘v b.) Circle the two diastereorners. MA; 3 How \ i é 0H c.) Circle the one that is a constitutional isomer of all the other structures. 5 3 K OH d.) Circle the two that are the same structure. gJN’ sfig OH x” t z R“ . .x " J ‘ Riki's m... , e.) Circle the meso structure. CHO CH0 g” CHO»: CH0 H OH H 0H 5 H OH? H OH H OH HO OH %.H OH; HO H CHfifil CH0 “x CH0; CH0 f.) Circle the compound that will have the higher boilingmpoint. butane f 1-propanol a .x M’ g.) Circle the compound that will have the lower boiling point. pentane (l 2-methylbutane h.) What force causes the compound in (f) to have the higher boiling point? t E" .n I ilk-Em a; \éxfiefiggm 3m \vflw d... M\ Chemistry 333 Exam 2 4. Let’s consider the Newman Projections of l-brornopropane (shown below). (22 points) CH3 y H H N Br H H Br a.) Looking along the C1-C2 bond we will define 0° when the bromide (Br) and methyl group is eclipsed. Draw the remaining Newman Projections in 600 increments for full rotation around the C1-C2 bond. ammmmm 120° 180° 240° 300° a b c d e f b.) Draw the relative energy diagram along 360° rotation about the C1-C2 bond. Oct. 12'“, 2010 same as a 360° (just use your knowledge of which conformations are higher in energy over other conformations to fill in the energy diagram) energy I 1 l 1 I | 0° 60° 120° ' 180° 240° 300° c.) Which conformation(s) have the bromide and methyl groups gauche to each other? (give the letter(s)) d.) Which conformation(s) have the bromide and methyl groups anti to each other? (give the letter(s)) am e.) How many diZZerent eclipsed conformations are there? 360° Chemistry 333 Exam 2 Oct. 12”“, 2010 4. Let’s consider the Newman Projections of l~bromopropane (shown below). (22 points) CH3 at H H N Br HH Br a.) Looking along the Cl-C2 bond we will define 0° when the bromide (Br) and methyl group is eclipsed. Draw the remaining Newman Projections in 600 increments for full rotation around the Cl-C2 bond. same as a 120° 240° 300° 360° c e f g b.) Draw the relative energy diagram along 3600 rotation about the C1-C2 bond. (just use your knowledge of which conformations are higher in energy over other conformations to fill in the energy diagram) energy 60° 1 20° 180° 240° 300o 360° c.) Which conformation(s) have the bromide and methyl groups anti to each other? (give the letter(s)) XIII: (1.) Which conformati0n(s) have the bromide and methyl groups gauche to each other? (give the letter(s)) e.) How many different eclipsed conformations are there? i) j Chemistry 333 Exam 2 Oct. 12"“, 2010 5. Follow the instructions for each part. (14 pts) a.). Give the IUPAC name for the following two compounds. 0% >J b.) In the following reaction, label the leaving group. (+3 9 Na S/\ if it: c.) In the following reaction, label the nucleophile. _t .t \ ' t 4? ” x.“ ‘31:: {‘“ngjfj; a t i i' e /\ ‘2 V’m‘h it, 41K fw’ ‘ R" W ix Na g S 3‘ 4 ‘ " /\ I R‘“«~§'K:;il,ijv,..r ’ “X My “ d.) Write the product of the following reaction. @9 N /\ 6.) Write the product of the following reaction. Mi... Pt Chemistry 333 Exam 2 5. Follow the instructions for each part. (14 pts) 31.). Give the IUPAC name for the following two compounds. b.) In the following reaction, label the nucleophile. H “m; ti _ MK. i d.) Write the product of the following reaction. NE? E>s”\ M» w_,r~‘"”fl‘\\ " " My" /\| e.) Write the product of the following reaction. H 2 l M —_—"—-——'> if“ ‘ Pt Oct. 12nd, 2010 Chemistry 333 Exam 2 Oct. 12nd, 2010 6. Follow the instructions for each section below. (6 pts) Br Br H Et Me H H CH3 H CH3 Me Et A B a.) How many gauche interactions does conformation A contain? M Wye .m‘ “K; b.) How many gauche interactions does conformation B contain? 5:3 c.) Based off of your answers from parts (a) and (b), which conformation is lower in energy, A or B? Extra credit: Draw the line angle formula for conformation above. Make sure you draw the correct stereochemistry using wedges and dashes. (3 pts) ti,”th if; 1:13? a M.I~\ ( 0M; x.» ‘0 t iii,” it 3 i? a m fir g ’39 M'fi' h" Chemistry 333 Exam 2 7. Follow the instructions for each part below. (12 pts) a.) Draw (lR)—tert—bu.ty1—(3R)-iodocyclohexane. b.) Is the compound trans or cis? c.) Draw the two chair forms of the compound in part (a). Make sure you transfer the chirality correctlyl! You do not need to draw in any hydro gens, just the tert-butyl and iodo group. Make sure your axial and equatorial positions are distinguishable to get full credit. (1.) If the 1,3-diaxial energy of a t‘ert—butyl group is AG = 4.7 kcal/mol and the axial energy of a iodo group is AG = 0.47 kcal/mol. Circle the conformation that is most stable. ' e.) If the Keq = 999, what percentage of the higher energy conformation is present at any one time? Oct. 12"“, 2010 .3 Chemistry 333 Exam 2 Oct. 12nd, 2010 7. Follow the instructions for each part below. (12 pts) a.) Draw (lR)-tert—butyl—(3R)—iodocyclohexane. their , M m. ‘2 r Mt {WA film,» 19.) Is the compound trans or 015? " R t at, .2? iv" e.) Draw the two chair forms of the compound in part (a). Make sure you transfer the chirality correctly!! You do not need to draw in any hydrogens, just the tert—butyl and iodo group. Make sure your axial and equatorial positions are distinguishable to get full credit. d.) If the 1,3-diaxial energy of a lert—butyl group is AG = 4.7 kcal/mol and the axial energy of a iodo group is AG = 0.47 kcal/mol. Circle the conformation that is most stable. e.) If the Keq = 999, what percentage of the lower energy conformation is present at any one time? " é Chemistry 333 Exam 2 Oct. 12nd, 2010 BONUS 21.) Specifically, what two energy strains cause the cyclopropane ring to have such high energy? (2 pts) b.) An SN} reaction proceeds through a carbocation intermediate. The carbocation is more likely to form when it is a tertiary carbocation. Please circle the compound that is more likely to undergo an SNl reaction. (Use your knowledge of tertiary carbons) (4 pts) \W>—Br /“Br H30~Br J in c.) What did Cody say to the guy at the review session with the funny voice? (4 pts) .r i.” ,~ x3 A x W, \i ,« m a”. .thtNKr" u \ {kcS Km" 1%); a {My MW a , It, ,r m- . a _ at 4A asks RA e, , it K t “v My.“ «:13? "%""”w~§;‘>~3 i“wi§;m"“\xa m We,“ h i t ‘ i ‘~~-~~§€M>t ...
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This note was uploaded on 03/05/2012 for the course CHEM 333 taught by Professor Lavigne during the Fall '09 term at South Carolina.

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Exam 2 key - Chemistry 333 Exam 2 Oct. 12nd, 2010 CHEM 333...

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