Chemistry 3720, Spring 2004 Exam 3 Name:

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1 Chemistry 3720, Spring 2004 Exam 3 Name: This exam is worth 100 points out of a total of 600 points for Chemistry 3720/3720L. You have 50 minutes to complete the exam and you may use the spectroscopy data sheet as needed. Good Luck. 1. (7 pts) Provide the major organic products from each step in the following reaction sequence P 3, ether Li P Na P , 2 6. Na, ether

2 2. (15 pts) Give the major organic product from each step in the following synthetic sequences. a. 1. +, 2 2. PCC, C 2 Cl m-cpba, C 2 Cl 2 b. 1. PCC, C 2 Cl 2 2. Na, 2, (C 3 ) 2 CuLi, ether followed by + quench c. 1. Mg, TF 2. + (quench) 1. Mg 2. PDC, C 2 Cl 2 d. 1. LDA, TF, -78 o C 2. C 3 C 2 1. Li 2. m-cpba, C 2 Cl 2 e. 1. +, 2 2. PCC, C 2 Cl Na xs Na, xs I 2 + CI 3 2

3 3 (15 pts) Give a complete mechanism, including important resonance structures for any intermediates that may be formed, that explains the outcome of the following conversion. Na, 2,

4 (10 pts) During the alpha-bromination of a ketone with 2 the reaction becomes acidic as is produced. Knowing this, and considering that the bromination reaction requires keto-enol tautomerism, give structures for each of the products or resonance forms found in the boxes in the following mechanism. 2 ( is produced as the reaction procedes) (8 pts) Provide the reagents needed to convert the given starting material into the product in the following synthesis. No need to show intermediate products CuLi in TF (quench) Li or Mg in TF 3 + (quench) 5. PCC, C 2 Cl 2 4

5 6. (16 pts) Give the major organic products from each step of the following synthetic sequences. a. 1. Li, ether Li 2. PCC, C 2 Cl 2 m-cpba, C 2 Cl 2 b Mg, ether Mg C 2 + (quench) C 2 Mg C 2 c. 1. s 4 2. NaI 4, Na Na, 2, NaCN, Et s CN d. Li 1. (C 3 ) 2 CuLi, TF (quench) Li, TF 3 + (quench) Li 5

6 7. (9 pts) For each of the following ketone/enol pairs indicate which you expect to be present most in solution. Explain your answers in terms of the factors governing the relative stability of each species. aromatic - more stable highly conjugated - more stable ketone more stable than enol (no conjugation in enol) 8. (10 pts) Rank the following in order of decreasing acidity; the most acidic =1, the least acidic = 5. Explain your choices. F F Cl C 3 F Electron-withdrawing atoms or groups in close proximity to the acidic proton will make that proton slightly more positive by pulling electron density away. Also, when the anion is produced (i.e. the conjugate base) it will be stabilized by electronegative atoms or groups since electron density will be pulled away through the single bond framework. 6

7 9. (10 pts) Provide a reasonable synthesis for the following alkene using the given aldehyde as the only source of carbon. You may use any reagents seen thus far in 3719/3720. (Show intermediate products but no need to show retrosynthesis). NaB 4 C 3 P 3 P3 Li (- =P 3 ) P 3 7