Midterm 1 - Page 2 of 11 f 7 Draw the skeletal...

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Unformatted text preview: Feb 26, 2009 Page 2 of 11 f 7- ) Draw the skeletal structures( (showing only C- C bonds) of all constitutional Isomers not write extra or duplicate structur- ! LW m (b) Which of the following molecules is represented by the Newman projection shown 0- the right: CH CHZCH ’ 3 (a)\jW\/\ (b) (0% (0 None of these (0) Draw all the possible Lewis—dot resonance forms for Ozone 03 in which the three oxygens are linked linearly. o (Bf-('39 9.. .153 .. Cfl—O/g (R3 :Oflo:0 Chem 3A Feb 26, 2009 Page 3 of 11 2. ( 15 Points) (a) Write a balanced equation showing starting materials, other necessary inputs, and products in the “Syngas” process. when Um by, uSQd 4w (d) Cracking of an alkane can sometimes produce some amount of larger alkanes starting from a smaller one. Show with detailed step-by-step equations how some hexane CeH14 might be formed in the high temperature catalytic cracking of a large amount of butane C4H1o. new?" u ‘4 god“ i? \l H t I I. r , A .l r I {A _ , ‘C-XL'“ “‘ '5 H “C. + C“ C C' H “J ' l r zeom-e ‘ l l \ r; P H U H 5" V \‘I Chem 3A Feb 26. 2009 Page 4 of 11 3. ( 15 Points) (a) Arrange the molecules below in order of decreasing boiling points. Answer: A > b > Highestlw. (b) Write clear Newman projections for (i) the highest energy conformation of pentane —> seen along the C2-C3 bond <— (ii) a Gauche conformation of butane seen along the 02—03 bond flit: ~ i «L~c»c, a C l ( ()1. (c) Write the electronic cOnfiguration of chlorine and show a fully labeled orbital energy diagram / u 5 Electronic configuration: \51 15” 1P 55" 3? Chem 3A Feb 26, 2009 Page 5 of 11 4. (18 Points) Structures and Nomenclature. Draw one of the two isomers of decalin in which the two 00 rings are in worm \* Draw the four-ring framework of steroids L Write the IUPAC name of the compound below 0 H \o a s .7 EH3 “Ha 3"“W‘l‘ CWCHZGHZEHZCHT—c (I: \rme" 4.- “MI La ’ nah—‘31 4 emt , 3 4 S— Mmefiwl - S'(1-_mem1\qwmfldewn¢ ’ I I Circle the structures below that represent molecules with substituents in a trans configuration Draw a clear structure for trans—1,3—dichlorocyclodecane r3 Chem 3A 5. ( 20 Points) Feb 26, 2009 (a) How many secondary hydrogens are in the molecule (CH3)[email protected]?CH CHZCH(CH3)2? it“: (A, Q *7, Answer. C“ -(T- a; chmtew; \ (b) What type of orbitals overlap to form the C- H bonds In the mlolegflgf ofteghene HZC= CH2 Answer: 329 0““ S ’t’ L (c) Write the Lewis-dot structure for the anion No; in which N is surrounded by three 0 24?, \/ \C’g; C’/\H (d) Circle the Wyou would expect to have a dipole moment of zero CHzClz 42, (e) An acid has Ka = 4.53 X 10*5 What is its Ke ? _ it Answer: Keq = XLMO—S +3 CH30I H20 Page6of11 VK keep? \e W one] =.H saw“ i553 (f) Give the hybridization of the central atom for each of the following structures and tell whether the shape of the compound is linear, bent, planar, pyramidal or tetrahedral? NH3 Hybridization: 39’ *1 Shape: X): vqmidoA 'll/( HCN Hybridization: $9 +/ Shape: Smear ! Z 'CH3 H Hybridization. 32L Shape. gonad 4’ ‘ H20 Hybridization: 323 ”f I Shape: ‘oen’c / Chem 3A 6. ( 14 Points) (a) Calculate the relative reactivity of tertiary vs. primary hydrogens for the imaginary halogen X2 given the experimental results obtained in the following monohalogenation. Show the details of your calculation. Feb 26, 2009 Page 7 of 11 'I. CHaH . CH3“ CHZH. 35 £ng mg l i Light l | | 1 r :3 "flew—CH3 + x2 —> "New + "SW—$4”: be = H on; H CH: x ca; [‘1 prim“ ‘ CompoundA 66% Compound B 33% reactivity of tertiary 3’. Answer: — = ‘ reactivity of primary (b) Write a balanced equation for the combustion of (CH3);CHCHZCH20HZCH20H20H3 (d) Hectane is the lUPAC name for the straight chain alkane with 100 carbon atoms (i) How many sigma bonds are there in hectane? 202 \4 Answer: SDl X% C” QrL~L+ qci L (H C; L 301 (ii) How many alkanes have an lUPAC name of the type x—methylhectane (where x is an integer) , ‘ 3 ' k (I , 2 Answer: l‘ / /, Chem 3A 7. (25 Points) (a) A Chem 3A student named Al Kane goes to purchase heating fuel and finds that both propane and cyclopropane cost the same price per Kg. Which fuel should Al choose for most value for money? Provide a short technical explanation of your answer. Feb 26, 2009 Page 8 of 11 (b) Write the mechanism of the following reaction including initiation, propagation and termination steps, calculate the AH° for each step and calculate the value of AH° for the overall reaction. Assume that the only mechanism of termination is the recombination of two Br radicals. I' ht HSC—CszCHa + Br2 L HgC—(IlH—CH3 + HBr Br Initiation: l/ H") \fiV Q ~ °_ YALN/ \ gy- fBr .———-—-§ B( + g( A\-\ v +45 ma Propagation: “ H\ ‘C. on Alf: Swim , 1.. H C— "‘ 3 BY 1+ Hgt—i‘éfi'CRS—H H 8" + 3 ' 6 h cows ‘03 u \4 . o- may i a - Mew B. . M. Psde—J‘fi Bi —" 3' H \ —1q.sv"’,}y . B W ’rqg V "f“ 3 Termination: Overall value for AH° = iii Chem 3A Feb 26, 2009 Page 9 of 11 8. (16 Points) (a) Consider the equilibrium below. Circle the most stable conformer and calculate the value of AG° for the change from conformer A to conformer B. (Discuss briefly the factors contributing to energy differences and show the details of your calculation) in Mfmu A. “‘3 has hm \i‘a'dzex‘w‘ _ e\ u us +9. 1.3-d-imc.at "Award D owi] rl“ mmkw «W,M \3 M in maxim 'imveWAi‘ *' m hqwor'mfi't “We“? w‘ml WM 8““ a. «an M 05 Rulmxm em (Mt—tumult ‘h B-‘WL (5;; 0? cm; x, w? H dew ”J Ma snug.- AG° = ”“7”. )(l/ (b) The energy difference between substituted cyclohexane conformers C and D is 40.8 Kcal mole‘1 calculate the equilibrium constant Keq at 300 K. Show the equation used for your calculation. AC; 03 u“ m‘ = 800 U W\ T7 59°“ , 2°“,va— Ag’; ,LTJLM‘W )(fi g (A; M L’9°%1 .3 on) k“ r. e RT = 6 Answer: Keq = 0164')( M 5 of gut (c) The equilibrium constant for the equilibrium E —“- F at 300K is Keq = 5.3 Calculate the percentage of F at equilibrium. ‘ Show the details of your calculation. ‘ X’L .5— = .943, . E \ F V a E;- X \Go - 5.3 6.5' l . : 84_ \3 /. Percentage of F at equilibrium— - 341% /- (d) Draw a clear stereochemical structure for (R) -2—butanol Answer: R (9 O\-\ l— - — 04 (kg)? @3 ( ‘ " 1 ‘\ _:rOH\\\H)</5 u at» a “ s "‘ ' QUE; D 0 (l) (3) ‘\\\\\—\® Chem 3A I Feb 26, 2009 Page 10 of 11 9. (15 Points) (a) the heat of combustion of cyclooctane 08H“; is 1270 Kcal mole‘1 while that of cyclohexane CeH12 is 944 Kcal mole‘1. Calculate the total ring strain per mole of cyclooctane. Show details of your calculations. _ ‘ .1, v‘ M magma: w c as C9 are 544%; assist/5 “I ‘ pa)“ C °4 (X H“, , \2'l0 3 z \53 JS \Lu ml g _ 63-19 4313 = H“, YA)“ Kn‘fisw" 'IS \‘4‘3 rd‘ PM L . . = LpA‘ _ Ring strain per mole of cyclooctane “Jo M +t,’ hay M3 6W“ 2 u») g Ll.4§)'—\\'b " (b) Which C-C bond would break first, the bond in ethane or that in 2,2-dimethylpropane? Explain. Answer: cat—A L-c. bent De ”“0: bond \n 1’7. dimmlmpmm)becau5¢, Ami brat/413A 4 N t L“ vital-c Mal.“ ‘4“ c-¢_, have. until ma Mm) W“ 30*?) “‘6“ a» _ flk‘C‘fi" one wring “=qu J m +. Z 2,1—dxo-W'QM em»... “mud M h“ cc“) r‘dchIer‘errrAh . . _ _ , (yea-mar ‘kcm 45m jun ‘WC=\S wuxd ba morn shabb- (d) Complete the followmg reaction showmg all monochlorination products, curcle the product obtained in greatest yield (EH3 N Cl H;C—CH~CH2—(|)H—CH3 ._2. ‘ - QH3 Light P” Ilfi‘ : \1- (H; +« L'\ WA ~ ‘ - ‘ our-C“ —C—(H—LH—-U\ + CH -C—0 5 ’LX“’ :3 CH3 l 7' l 3 5 I ' ‘ “4-way; CI (H3 (“5 “ CH3 ’1 x; c \0 (e) Name the following according to IUPAC Nomenclature K CH onscuzcu}<§-CHZCH3 ‘ ‘ C R)- 3- mew-.ihexcme. (D G ® (f) A solution of 0.2 9 mL‘1 of an unknown sugar in water in a 20 cm polarimeter cell cause a clockwise optical totation of 8.23 Calculate thespecificrotation of the sugar Answer: Specific rotation ° /k l 10¢ Chem 3A Feb 26, 2009 Page 11 of 11 Note: There are no questions to be answered on this page, it only contains data that may be ofuse in solving the questions contained in this exam, Not all of the data given is needed. vaeofgas constant: R = 2.0 cal K’1 mor1 Value of absolute zero (kelvin) = —273°c Vale of e (base for natural logarithms) e = 2.718 Density ofgasoline : 0.8 9 mL‘1 [”201 = 55 me '51 Bond dissociation energies (in kcal mole'1): RCHz—H 101; Rch—H 98.5; R3C—H 9&5; Cl—Cl 58; Br-Br 46; 1—1 36; H—Cl 103; H—Br 87; H—1 71; RCHz—Cl 84; RCHz—Br 70; RCHz—l 56; RZCH-Cl 85; RZCH—Br 71; R3C—Cl 85; Rac—Br 71; CHa—H 105; CHa—I 57; CH3—Br 70; CH3—CI 85; Hac—CHs 90; CH3CH2—CHZCH3 88: (CH3)3C—CH3 87; (CH3)3C—C(CH3)3 78.5 Values of strain energies: 1 Each CH3 - H eclipsing interaction: 1.5 kcal mol' Each H — H eclipsing interaction: 1.0 kcal mol‘1 Each CH3 - CH3 eclipsing interaction: 2.5 kcal mol‘1 Each CH3- CH3 gauche interaction: 0.9 kcal mol'1 Each t—Butyl - CH3 gauche interaction: 2.0 kcal mol'1 Each CH3 — H 1,3-diaxial interactio '1, cal mol‘1 Each Cl - H 1,3-diaxial interaction: . cal mol‘1 Each CH3 - CH3 1,3-diaxial interaction: 1.6 kcal mol‘1 Each H - CN 1.3-diaxial interaction : 0.1 kcal mol'1 Each H - C(CH3)3 1,3-diaxial interaction: 2.5 kcal mol'1 Partial periodic table of the elements 1 2 - 1.00790 1.00260 3. 4 5 5 7 9 . o I Be B C N O F Ne 6,9 1 0.0121! 10.111 12.011 14.0087 15. 4 10,9 84 20 9 0 8 . s 1 9 . 7 1 4 . 5 3 8 i 9 7 11 12 13 1d_ 15 15 1 3 M9 Al 81 P* S l ' Ar 22339; 34.3050 26.9015 28.0855 30.9738 32.066 35 527 J 918 19 20 31 32 33 34 a s 5 Ca Ga Ge As Se Br Kr 39.0903 (0.07! 69.723 72.61 70.9216 .7036 19.904 03.6 ...
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