Chemistry 14D Winter 2016 Midterm Exam 1 Page 1

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1 Chemistry 14D Winter 2016 Midterm Exam 1 Page 1 OK to use "" anywhere on this exam where appropriate. Exceeding the specified word limit on an answer will result in a point deduction for that answer. t is not necessary to draw transition states unless requested by the question. 1. (6) Captopril is an antihypertensive drug. The last step of its synthesis is an S N 2 reaction: X O N CO Nucleophile Solvent Write the name or structure of a specific molecule in each blank. Example: " O - " might be an acceptable answer, but 'nucleophile' is not. (a) This reaction is fastest when X is. (b) The reaction is fastest when the nucleophile is. (c) The reaction is fastest when the solvent is. S O N CO Questions 2 8 refer to this S N 2 reaction of 2-chlorobutane: Cl ( C 2 C 2 C 2 ) 4 N + - acetone 2. (2) Circle all of the correct representations for the transition state of this reaction. δ C Cl δ 3 C C 2 δ - C Cl δ 3 C C 2 Cl δ - C 2 δ Cl C δ C 3 C C 2 δ - 3. (2) Circle all of the correct representations for the product of this reaction. 3 C 4. (2) When the starting material is a mixture of 80% (R)-2-chlorobutane and 20% (S)-2-chlorobutane, the absolute configuration of the product is (circle one): All S Mostly S with some R An equal mixture of S and R Mostly R with some S All R 5. (10) Consider the effect on the rate of the S N 2 reaction when the following changes are made. n each blank write 'slower', 'faster', or 'no appreciable change' as appropriate. The changes are not cumulative; for example the change in part (b) does not also include the change in part (a). (a) odide ion change to triflate ion ( - OSO 2 CF 3 ): (b) Chlorine changed to triflate: (c) odide ion change to fluoride ion: (d) Ethyl group of 2-chlorobutane changed to ( ) 3 C group: (e) Acetone changed to methanol: Page 1 score =

2 Chemistry 14D Winter 2016 Midterm Exam 1 Page 2 6. (2) Methanol has ε = 33 and ethanol has ε = 25. n the box write your best guess for the ε of C 2 C 2. Answer choices: 38, 29, or (3) Based on your answer to question 6, circle the property or properties that best describe C 2 C 2 : Aprotic Protic Nonpolar Moderately polar ighly polar 8. (10) ( C 2 C 2 C 2 ) 4 N + - is soluble in both acetone (ε = 21) and acetonitrile (an aprotic solvent; ε = 38). Let's figure out what happens to the rate of the reaction on page 1 when the solvent is changed from acetone to acetonitrile. (a) When the solvent is changed from acetone to acetonitrile, what happens to the energy of the reactants? n the space below write 'increased', 'decreased', or 'no significant change'. (b) When the solvent is changed from acetone to acetonitrile, what happens to the energy of the transition state? n the space below write 'increased', 'decreased', or 'no significant change'. (c) When the solvent is changed from acetone to acetonitrile, which experiences a greater change in energy? n the space below write 'reactants', 'transition state', or 'change about equal'. (d) ere is an energy profile for the reaction when the solvent is acetone. Draw a colored (not black or red) or dotted (any color except red) line to show the energy profile when the solvent is acetonitrile. Be neat and precise. Practice your answer on the back of the exam page before you draw your final answer here. Energy Acetone Reaction coordinate (e) Based on parts (a) (d) of this question, we can now make a conclusion about the rate of the reaction in acetone versus acetonitrile. n which solvent is the reaction faster? n the space below write 'acetone', 'acetonitrile', or 'rates about equal'. Page 2 score =

3 Chemistry 14D Winter 2016 Midterm Exam 1 Page 3 9. (3) n the box draw the most likely rearrangement product of the carbocation shown below. nclude curved arrows. 10. (2) n addition to the rearrangement of question 9 there are two more common carbocation fates. Write the names of these two fates. Fate name: Fate name: Questions refer to this reaction: Cl 3 C Molecule A 11. (3) n the box above draw the major S N 1 product from the reaction of molecule A. 12. (6) Write the mechanism for the formation of the product you drew in question (6) Consider the effect on the reaction rate when the following changes are made to the S N 1 reaction of molecule A. n each blank write 'slower', 'faster', or 'no appreciable change' as appropriate. The changes are not cumulative; for example the change in part (b) does not also include the change in part (a). (a) changed to C 2 C 2 : (b) Ethyl group changed to phenyl group: (c) odine changed to chlorine: 14. (6) Complete two distinctly different reasons why the reaction of molecule A does not occur by an S N 2 reaction. Add no more than ten words in each case. f there is only one reason write "no other reason" for part (b). (a) This reaction does not occur by the S N 2 mechanism because... (b) This reaction does not occur by the S N 2 mechanism because... Page 3 score =

4 Chemistry 14D Winter 2016 Midterm Exam 1 Page (9) Draw three additional organic products (not necessarily limited to S N 1) likely to be formed in the reaction of molecule A. (Organic products contain at least one carbon atom.) Products that are less likely earn less credit. f three additional products cannot be drawn, draw an X through each box that is not used. 16. (7) Consider the ionization of molecule B: + B C D E For each possible product, write "is" or "is not" in the blank. f you wrote "is" you are done with that possibility. f you wrote "is not" complete the explanation by adding no more than ten words in each case. You must use a different explanation in each case. C the most likely ionization product because... + D the most likely ionization product because... E the most likely ionization product because... Br C (2) Circle all the terms which apply to the molecule shown: Cis Trans E Z C C Cl 18. (2) Draw in the box the most stable alkene of formula C Page 4 score =

5 Chemistry 14D Winter 2016 Midterm Exam 1 Page (11) The dehydration (loss of water) reaction shown below can produce at least three different alkene products. Draw the mechanism for the formation of the most likely alkene product. Draw a box around your final product. 3 C aq. 2 SO (6) Using no more than ten words in each case, write three distinctly different reasons why the reaction shown here probably cannot proceed via an E2 mechanism. f there are less than three reasons, write "X" after each of the reasons you are not using. F C( ) 3 C 2 C 2 Reason #1: Reason #2: Reason #3: Page 5 score =