CHE 118A SampleMt1Key

CHE 118A SampleMt1Key - Page 1 Chemistry 118A Name First...

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Unformatted text preview: Page 1 Chemistry 118A Name First Midterm Student ID No. Fall 2002 October 24, 2002 1. Please write the name of your TA. '22- m This exam contains 5 pages and 4 problems. ' When you are told to start, check to see that all the pages are there. If not, ask for help w. No adjustments will be made later. 1. ( 12 pts) Draw a structural formula, your choice of Lewis, Kekule, condensed, bond-line, etc.) corresponding to each name below. Provide a systematic name corresponding to each structure below. (a) 3-ten-butyl-2,2-dimethy1hexane (b) sec-butylcyclopentane ~ 6I (0/ é“+r\ICLLON'S.WfL7I“3-OIW1L7le’f47O‘ £1— lA—LXQM o( (d) +thS~ L lat/owe ’3 4,3014) CyCLOI/LQKGML Page 2 2. ( 28 pts) Answer according to the directions for each part. (a) Write Lewis structures for HOCN and HNCO (cyanic and isocyanic acids). zww H—b-Csmfl H,H=C=5, mahg ‘ (b) Cyanic and isocyanic acids are (circle the correct answer) Q ’} resonance constitutional stereoisomers p 5 forms isomers (c) Reaction of either cyanic or isocyanic acid with base forms cyanate ion. Draw at least two difierem possible Lewis structures for cyanate ion. Circle the best one. 220w ,_ .. u wtfib :NZC‘05 (d) The Lewis structures you drew in part (c) are (circle the correct answer). (Q + resonance constitutional stereoisomers p 5 forms isomers (e) Cyanic and isocyanic acids equilibrate (interconvert) in water solution. Using curved two—electron arrows show in detail how cyanic acid turns into isocyanic acid, step—by- step (the process requires more than one step; cyanic acid has a pKa of 3.7. '0 Iv . A + __.. A HO:/'$ H_OLC5N1v<-;* H3O f ('Qgcgnj: m 1 '3”) do” " ‘5"; \"'O“H ( [47.73 + 10:C:t\1’-H + (f) Ammonia, NH3, has a pKa of 35. What is the geometry of ammonia, and what is the hybridization of its nitrogen atom? J] L ' Mia aefldq SF3 (4+fi4) Page 3 (g) Acetamide, CHjcrfsin , has a pKa of 17. Explain why the pKa of acetamide is so much lower than the pKa of ammonia. 7%. 0633303 LM [‘5 Slag/«7:24 ETC/M 'Q 3 +3 rem r 5-0"(1"“ {0% P CO Cat/$0"! M ‘4) “"01 '[CH3~3*Q/H H CHj’C’LS'NH (h) What is the geometry'and the hybridization of the nitrogen atom in acetamide? Q Q (A 47?qu 3,21 (t; 4:114:14 11’ 50*»! “1 A” D (4, VMMV‘ 3. ( 24 pts) (a) Complete the following equation by writing the structures of the products of the monobromination of 2,3-dimeth lbutane: y CH3 C H} cm FH3 A ) I A ers H3C—CH—CH—-CH3 + 13:2 H3 cic'; r CH ——ch + H gr E 4153/ +2r+lavyj Br (b) Write out the two propagation ste s in the mechanism for the reaction in part (a). (EH3 (alw/ ,CH; 9%; 01‘ 8" HJC"C-*CH"CHJ "T7 HBW —r CHyg‘A CHACH] A m K) I A ‘ (8 khl’> L/H\ (my 9],, C”; Cw @Zpfi 9H3 (CH3 I I H3C— Br’gr '—3 1- gf‘ ' 4 \ a . v 46 71/!)3 @ 219%; (c) Calculate AH° for each of the propagatiion steps in part (b), and AH° for the overall reaction in part (a). Use these AH° data: I ((9 Brz = 46 HBr = 87 Primary CH = 101 Primary CBr = 70 + 9. 5’ Tertiary CH = 96.5 Tertiary CBr = 71 (all in kcal/mole) ‘ x 45 .5 kcal / (L 520;}! ((1) Compare monobromination of 2,3-dimethylbutane with monochlon'nation of the same alkane. In what way would they differ in (i) relative rates Cu Lo r 1 am ,5 rum/la {am .A (ii) number of organic products formed in significant quantities (iii) suitability as method to prepare (synthesize) a single organic product. DCLboréuaahiw 34M more— fowdradj (2 vs. ( Ar» évo’z/méoaib'yj 13 0t 3004 MW “to ’H‘x, {ewfiénj WodeI/Lc. as an almm‘ excl/angle Peozaxacfflirjl, 7120/) 4. ( 36 pts) Multiple choice. Circle the correct answer (a) Contains an ionic bond CH3CC1 ‘ CH3C1 CCI4 None of them (b) Contains an ionic bond H20 H2SO4 None of them ‘ (c) Strongest Bronsted (proton) acid ‘ H20 @ BH3 ‘ CH4 NH3 (d) Is a Lewis acid H20 H28 CH4 NH3 (e) Has the highest boiling point &»Mw@ (f) A pair of resonance forms + C.” C. .. '- H2C=N=N= H—§1=9: :0: d H 7' Itl N d H.641 d an C— E : an : 2 .. C. an Page 5 (g) Contains a nucleophile carbon atom. _ gBr CH3C1 C02 CH3C02H (h) Not a Lewis base (CH3)2NH H2C=O H20 HNo2 (i) Is a transition state eclipsed gauche chair methyl ethane butane cyclohexane radical (j) Most stable radical :5 5; <5 5;. (k) Reason cycloalkanes with more than three carbons in the ring are nonplanar eclipsing van der Waals angle relativity force strain (1) Energy minimum for 3-methylhexane around the C2-C3 bond. H3 H3 CH3CH2CH2 H CH2CH2CH3 H H CH3 CH3CH2CH2 CHZCH2CH3 ...
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This note was uploaded on 06/07/2011 for the course CHEMISTRY 118 taught by Professor Nasiri during the Spring '11 term at UC Davis.

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CHE 118A SampleMt1Key - Page 1 Chemistry 118A Name First...

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