Chem+8A+midterm+3+key+Fall+2009

Chem+8A+midterm+3+key+Fall+2009 - Name Last First(PLEASE...

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Unformatted text preview: Name: Last, First (PLEASE PRINT CLEARLY) CHEMISTRY 8A Fall 2009 Midterm Quiz 3 November 25, 2009 Professor Sheila S. David 1. 2. 3. _ 4- 5. 6- 7. _ 8- 9. —— Total Extra Credit For students to read at exam time: Closed book and notes. Please read exam carefully. Partial credit may be awarded if you show your work. For students to read after exam is returned: If you have any problems with the grading of a question, return your exam to Dr. David/TAs by Dec. 7 with a note attached indicating which problems should be regarded and a brief explanation. Regrades will not be accepted after Dec. 7. ID Check E] Student ID Number: Name: (PLEASE PRINT CLEARLY) 1. (20 pts/4 pts each) Appetizers/ Multiple Choice—Put answer in the box at the right (i) For the following pair of compounds, which compound has a more nucleophilic nitrogen? o 9 o o 9 “Min: vs H30“: = f'i H A B (ii) Indicate thich of the carbocations in the following pair is more stable. /\CH2 vs /\/CH3 / ® (+3 A B (iii) Which of the following correctly describes intermediates and/or transition states? A) Transition states occur at minima 0n reaction coordinate diagrams O B) Both transition states and intermediates occur at maxima on reaction coordinate diagrams C) Transition states have partially formed bonds whereas intermediates have fully formed bonds D) none of the above (iv) Consider the following reaction: HBr /\/———>/\( Br What is the stereochemistry of the product(s)? Uta/3m (5 A. B. C. 0% R, 50% S (v) Which of the following compounds will react most rapidly with HCl? A) 5-methyl-l-hexene B) 4-methyl-1-hexene C) (E) 5-methyl-2-hexene D) (E)-2-methy1-3-hexene Obi} E) 2-methyl-2-hexene /\\/\ 3 M\ \/\/ ./\ L93 E Name: ~ Last, First (PLEASE PRINT CLEARLY) 2. (8 pts) Fill in the blanks: a. Stereoisomers with an asymmetric carbon center and e n a H’HD W t/$ non-superimposable mirror images are called: ohtfl b. Equal amounts of two enantiomers is called a W m g m filibW/ MM (#102 M c. lsomers that differ in connections between atoms are called \ c OonS/IU'iMbMqus 0 Mai/3 d. The interconversion of a single enantiomer into a racemic mixture is called: . m (Le WM 501be 3. (12 pts) Indicate whether each of the following molecules is more likely to behave as a nucleophile (N) or electrophile (E): /C/CH3 H’Cé BF3 3'9 H I (.9 /_ 0 /N\ “3" C“3 O NaOJTkCHs E 4. ( 6 pts) What is the carbon building block that can be used to synthesize the following alcohol or alkyl bromide? IE H+, H20 H3C/\/kCH3 HBr \ Br “acme” 5. (6 pts) Give the two products that would form in the hydrobromination shown below Br Br . major minor AA 3 Name: Last, First (PLEASE PRINT CLEARLY) 6. (12 pts) Polymers: better living through chemistry. A) Draw short segments of the polymer obtained from polymerization of l-pentene with Hi \WV‘J’MJL f M k/(F j,— 2 B) In alkene polymerization using H, the H+ is usually generated from mixing Bl:3 with H20 which react to form [F3BOHI' and Hi Explain (by showing chemical reactions and structures) why HCl and HZSO4 cannot be used as the acid source for these reactions. Mum WM) W iggfiuu 04 tint/Mo will jive W amok"), % Name: Last, First (PLEASE PRINT CLEARLY) 7. (18 pts) A reaction feast Draw the structure of the MAJOR organic reaction product produced in the following reactions. If no reaction takes place, write NO REACTION. You do not have to balance the equation. BE SURE TO SHOW ALL STEREOCHEMISTRY. \ 035W catalyst /\ H2304 + OH ————> 0V HgSO4/ sto4 H———_=—\ ———-> H20 HBr Name: Last, First (PLEASE PRINT CLEARLY) 8. (14 pts) Killing me softly Metolachlor is a liquid herbicide used for many crops. In 1996, it generated sales of $450 million, making it one of the most popular pesticides on the market. Metolachlor kills weeds by preventing the plants from making a waxy coating on the leaves. This wax is produced with the help of an enzyme called fatty acid elongase. When the enzyme activity is inhibited, the wax is not produced and the weed dies. The following graph shows the amount of R— and S- metolachlor required to interfere with the enzyme. 100 ‘ " ~l 0 CH3 2:? ~ CI /K/OCH3 75 I a Fatty Acrd N ’X a; l Elongase H c '9 50 g 3 CH3 ‘0 E l I 25-1 [:3 S~Meto¢achlw Meto|achlor I R'Melolachlor U o Jr-wv—W-v—r. vwrw~1fifl c; or 1 10 10C «sou Metolachmr WM} A) Identify the asymmetric carbon center in metolachlor and label it with an asterisk on the drawing above. B) Draw and label each enantiomer of metolachlor (use dash/wedged lines to indicate stereochemistry). D b \L//Uf3 \ / / / 'J z t, C/ x I U C “.3 ¥ \ W} 650 m \CH OCH 0 W L 3 93 \ “W5 C) Based on the graph data, if you wanted to kill weeds which enantiomer would you use? D) Why do these enantiomers have different activities? El 9. Name: Last, First (PLEASE PRINT CLEARLY) (14 pts) Reactions and Mechanisms: Electrons and arrows A) Complete the following reaction and draw a step—by—step mechanism for the reaction. HBI’ B F B) Draw a reaction coordinate diagram for the reaction above. Draw structures of the reactions, products and intermediates in the proper places on your diagram. 6?) Name: Last, First (PLEASE PRINT CLEARLY) Extra Credit (10 pts max possible) In class we discussed the mechanism for polymerization of ethene using BF3 as an initiator to yield polyethylene. Another method for promoting polymerization is to use an alkyl peroxide (ROOR) to initiate a radical polymerization cascade. A) illustrate the chemical mechanism (using chemical structures) for radical polymerization of ethylene using ROOR. Show arrows, electron movement and monomer addition in your mechanism. in thwhm 3 (PVC “OP— ”‘a a w /A 'N QCCAL/L f4 OH;ng “a P 0 fl .____._____? ml“ o/‘Q‘ Cliff L- Q 0 “ab/(flatly? fr”? .1 Wow ’ waalywywyfiiqluafi Name: Last, First (PLEASE PRINT CLEARLY) B) Low-density polyethylene (LDPE) which is used for fruit and vegetable bags at the grocery store contains highly branched polyethylene and is usually prepared using a radical polymerization method. Based on the mechanism for radical polymerization you showed above, show with chemical structures branching of the polymer chain may occur. Show arrows, electron movement and monomer addition in your / BO wwj V5»? M . CHI/(J V/a bra/Wu: - A! C) Suggest a reason why radical polymerization provides more branching than mechanisms using an electrophilic initiator (i.e. BF3 or H*). ...
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Chem+8A+midterm+3+key+Fall+2009 - Name Last First(PLEASE...

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