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Sample Exam3_Key - Chemistry 2521 Fall 2007 Midterm 3 Exam...

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Unformatted text preview: Chemistry 2521 Fall 2007; Midterm 3 Exam This exam has 7 problems on 9 pages. Make sure your copy is complete and correct, Printed Name (Last, First) K 6C? Scores: Problem 1: 0 Problem 2: H? Problem 3, M Problem 4‘ Z 0 Problem 5. LE Problem 6. q Problem 7. Total: / fl W 1. (10) Using provided boxes, answer the questions on mechanism of the following reaction: light (hv) :/—Br + H8:— _ / + Brl Using the 'fishhook" arrows write the initiation step in the reaction mechanism (2 pts): light (hv) Using the "fishhook" arrows, write the two chain propagation steps in the reaction mechanism (6 pts): Z/‘n—O V‘N_Br IFI/Vlg/f/ :/' + HBr (3 pts for arrows) allyl radical (3 pts for arrows) Using "fishhook" arrows and showing the structure of the second resonance contributor, show resonance stabilization for the allyl radical (2 pts): allyl radical (1 pt for arrows) resonance contributor (1 pt) 2. (10) Answer the questions on mechanism of the following reaction: OH C1 + H20 + H30“r + Cl" H20 a) Which of the following energy diagrams best represents the course of this reaction (circle the 2 a L 4 fl Ieadion readi on reaction coordlnate coordinate coordinate correct answer, 3 pts)? L reaction coordinate energy energy energy b) Circle the correct rate equation for this reaction (3 pts): Rate = k x [RX] x [H20] Rate = k x [in x [Cl’] Raw = k x [H20] x [CH C) Circle the nucleophile in this reaction (2 pts): d) Circle the carbocation intermediate in this reaction (2 pts): [email protected]@“ 3‘ (20, 4 pts each) Circle the structure of the major product in each of the following reactions: /\ ‘I § \\ f 2—methyl-l -pentene 2—methylA137pemadiene 2~methyl»1-penten—4—yne (2-methyl-1-pemen-3—yne ) 5—methyl—2—pentyne 5-melhyl-2-pentyne NaNHz (1 mol) c1433: (1 mol) 1. BH3.THF NH: 2. H202, NaOH OH 0 & no“ (b) HCECH ifim 4—br0mocyclopenlene 1-bromocyclopemene 3-bromocyclopentene bmmocyclopemane tram-l ,2-dibromocyclopenxane ’W‘ L '1 (CH ) C L' (2)727pentene (E)-2-pentene u 1 3 2 ‘, 2-methylbutane 2-methyl-l‘butene (d) W1 ether 2-methyl—27pentene 1-pentyne H CN HQH /\/\ H,’OH " M 4, (20; 5 pts each) Draw the structure of the main product for each the following stereoselective reactions. Draw structures in the provided boxes; make sure to show the correct stereochemistry for the substituents (72 pts for wrong stereochemistry). TosCl NaSH CH OH 0/4 / 3‘0; pyridine acetone 3 4/ 5 [1/ Ph CH 0H HSC\%LBr 3 methanol _ HZ, Lindlar catalyst \ / W Brz (1 mol.) — c1-12c12 5. (16, 2 pts each) Place in each box the molecule of a reagent that is required to perform each of the following reactions: N55 .5 W O “a ; ether arc/’61 ‘r 6H)“ H20 755 CZ (>7 OH I . (>7 OTos pyridme 6. (9 pts) (a) Assign the RS configuration to each stereocenter in the following compounds (1 pts each stereocenter', use the provided circles for your answers): HC (3) 3 t \® (b) i am (b) Using provided stereocenter, finish the drawing of (S)-2,3-dimethylhexane by placing appropriate substituents in the boxes on the bonds: (2 pts each substituent): ' {Vlad/l7, Hu‘f" Z Fl’; 6 M H3C af‘C/f; \ CH3 7. (15, 5 pts each) For each of the following questions (a)-(c) circle the item that is the correct answer, (a) Which one of the following molecules is chiral? pm 6’ ix (b) Which of the following alkyl bromides reacts the slowest with sodium cyanide, NaCN, in dimethylsulfoxide? 1-bromo-2—methylbutane 2-bromo-3-methylbutane 1-bromobutane 1-bromo-2,3-dimethylbutane bromomethane bromoethane (c) Which one of the following compounds has the best leaving group? cyclohexanol 3—methylcyclohexanol l—methylcyclohexanol iodocyclohexane methylamine chloromethane fluorocyclohexane 2»bromohexane ethanol ...
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