1NAME _______________________ ID # _______________________ ORGANIC CHEMISTRY I (2301) 9:30 – 10:20 am, July 11, 2011 Exam 2 Form A If you want to pick this exam up on Tuesday in class (in public), please check the box on the right: If you do not check the box, I will not bring your exam to class on Tuesday, and you will need to pick up your exam in private from Chemistry department staff in 115 Smith beginning Wednesday, July 13th. Exams that are not picked up within two weeks will be disposed of. A periodic table is attached to the back of this exam as an aid. Otherwise, you are not permitted to use any other materials (including notes, books, or electronic devices of any kind). Right now, write your name at the top of this page, and fill in the bubbles on the multiple-choice answer sheet for your name and your 7-digit student ID number (in columns 1-7 of the “Identification Number” section, as shown at right). When the exam begins, also write your name at the top of page 4. You may use pen or pencil. However, re-grades will be considered only for exams completed in pen. Please write your answers in the bubble sheet for the multiple choice portion of the exam, and in the boxes/spaces provided for the written portion. If your answer is not in the appropriate space in the written portion (say, for example, it’s on the back of the page), draw us an arrow and/or note telling us where to look.2Multiple-Choice Problems Please answer these problems on the bubble sheet. (2 pts each) For each of the molecules drawn below: - For each atom marked “chirality”, indicate whether the atom would be labeled as (a) an (R)-chiral center, (b) an (S)-chiral center, or (c) not a chiral center, according to the Cahn-Ingold-Prelog classification system. - Indicate whether the molecule would be chiral or achiral. Mark each answer on the bubble sheet, with the problem number indicated inside each box. (2 pts each) Each reaction below is drawn with multiple potential products. Of these products, which would you actually expect to observe? Keep in mind that, for each reaction, you might predict one, multiple, or none of the products shown. HHBrBrchirality #1 chirality #2 chirality #3 chirality #4 5. Is this molecule a. chiral, or b. achiral? FNaCN CN14. a. Yes, or b. No? + 13. a. Yes, or b. No? Would you expect this product? chirality#6 OCH3HCH3HH3CH3Cchirality#7 8. Is this molecule a. chiral, or b. achiral? HO CH3H3C OHOOH3CCH3chirality#10 chirality#9 11. Is this molecule a. chiral, or b. achiral? + 12. a. Yes, or b. No?3 18. (3 pts) Are the two structures below 19. (3 pts) Are the two structures below 20. (3 pts) Are the two structures below Multiple-choice problems 21 and 22 are at the end of the exam, on page 7. CH3CH3+ 16. a. Yes, or b. No? a. enantiomers, b. diastereomers, or c. the same molecule? CH3FFCH3H3CFFCH3a. enantiomers, b. diastereomers, or c. the same molecule? ClBrHH3CCH3HCH3H3CHClBrHa. enantiomers, b. diastereomers, or c. the same molecule? H3CCH3CH3CH3ClH3CCH3CH3OCH3H3CH3CH3C17. a. Yes, or b. No? Would you expect this product? H3CH3CH3CO NaCH3CH3+ 15. a. Yes, or b. No?4NAME _______________________ Scoring: 23. _________ / 12 24. _________ / 24 25. _________ / 15 Total Score: _________ / 51 23. (12 pts) For the reaction shown below, draw a mechanism that explains how the product is generated from the starting material. In your answer, make sure that you: - Draw each step of the mechanism separately; - Use “electron pushing” to show where the electrons in each step go; - Use only the molecules that you are given; do not invoke reactants or solvents that aren’t in the problem. OHH2SO4 524. (15 pts) Draw the missing reactant or product in the empty boxes. For products, give the predominant, most favored product. Illustrate stereochemistry in your answer where appropriate. For reactions that yield multiple enantiomers, draw only one enantiomer in the box, and include the note “+ enantiomer”. CH2CH3HCH3BrKOH an alkyl halide (as the major product) S KH HH3C BrNaOCH3625. (24 pts) The triflate group (CF3SO3-) is such a good leaving group that alkyl triflates will undergo nucleophilic substitution reactions even with poor nucleophiles, such as chloride ions. For the reaction of the triflate shown above, both SN1 and SN2 mechanisms occur, and some of each product enantiomer would be generated. We’ll assume that the rate of SN1 and SN2 reactions are exactly equal. a. In the boxes below, draw mechanisms that explain how the products above are generated from starting materials via SN1 and SN2 reactions. In your answer, make sure that you: - Draw each step of the mechanism separately; - Use “electron pushing” to show where the electrons in each step go; - Use only the molecules that you are given. Feel free to add arrows, any necessary electron pairs, and intermediates directly to my drawings. Ignore stereochemistry for this part of the problem. + + [] = -23° (rotates polarized light counterclockwise) [] = +23° (rotates polarized light clockwise) + ClO SOOCF3CH3CH2CH3H(S)CH2CH3CH3H(R)ClCH3CH2CH3HCl(S)OSOOCF3SN1 mechanism: SN2 mechanism: ClO SOOCF3CH3CH2CH3HClO SOOCF3CH3CH2CH3HOSOOCF3ClCH2CH3CH3HOSOOCF3ClCH2CH3CH3H7b. On the diagram below, draw potential energy curves for these two mechanisms. (I have already drawn the energies of starting materials and products; you need to connect them with curves. You do not need to draw transition-state structures.) Make sure your curves illustrate the relative energies of the rate-determining transition states for the two mechanisms. Answer the following questions on your multiple-choice bubble form. 21. (3 pts) Once the reaction above is complete, and all of the starting material has been converted to products, the product mixture would a. rotate polarized light counter-clockwise; b. rotate polarized light clockwise; c. not rotate polarized light. 22. (3 pts) What would happen if iodide (I-) were used as the nucleophile instead of chloride? How would the stereoselectivity of the total reaction—that is, the preference for one product enantiomer over the other—change? a. The stereoselectivity would decrease. b. The stereoselectivity would increase. c. The