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Chapter 14

Chapter 14. ALKENES AND ALKYNES II. First part of the chapter only pages 14-1 through 14-23 (Skip Sect. 14.3) OXIDATION AND REDUCTION OF ALKENES. What is Oxidation?. Loss of electrons Gain of oxygen atoms Loss of hydrogen (H 2 ). INCREASING OXIDATION.

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Chapter 14

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  1. Chapter 14 ALKENES AND ALKYNES II First part of the chapter only pages 14-1 through 14-23 (Skip Sect. 14.3) OXIDATION AND REDUCTION OF ALKENES

  2. What is Oxidation? • Loss of electrons • Gain of oxygen atoms • Loss of hydrogen (H2) INCREASING OXIDATION

  3. What is Reduction? • Gain of electrons • Gain of hydrogen atoms • Loss of oxygen atoms REDUCED

  4. Problems 14.1 (structures on page 14-4) 14-2, 14-3, 14-4b, 14-6, 14-7, 14-8

  5. Sect. 14.1 EPOXIDES anti-glycol formation

  6. MAKING EPOXIDES Bromohydrin (Chapter 8) ( peracid )

  7. Carboxylic Acid Hydrogen peroxide Organic Peroxide A PERACID

  8. anti-Glycol Formation EPOXIDATION anti ring opening RING OPENING

  9. Sect. 14.2 syn-GLYCOL FORMATION

  10. syn-Glycol Formation (I) osmium tetroxide syn hydroxylation

  11. MECHANISM Notice the transfer of 2e- onto Os = REDUCTION OXIDIZED Both of the hydroxyl oxygens in the glycol come from OsO4 REDUCED

  12. SYN ADDITION GIVES CISGLYCOLS C H 3 C H H 3 H O 2 O H O s O 4 H O H

  13. syn-Glycol Formation (II) potassium permanganate syn hydroxylation

  14. Skip Sect. 14.3

  15. Sect. 14.4 OZONOLYSIS

  16. OZONE electric discharge or cosmic rays .. .. .. .. : .. .. .. - + + : : .. .. - EQUIVALENT RESONANCE STRUCTURES

  17. Ozonolysis

  18. WORKUP PROCEDURES FOR OZONOLYSIS Two types of workup (decomposition of the ozonide) are possible : 1. OXIDATIVE Hydrogen peroxide is present Aldehydes are oxidized to carboxylic acids. Formaldehyde is oxidized to carbon dioxide, which is lost as a gas. 2. REDUCTIVE Add Zn and H2O or H3O+ METHOD A Reduce the ozonide with Pd / H2 , and then add acid ( H3O+ ). METHOD B Aldehydes survive intact and are not oxidized with reductive conditions.

  19. REDUCTIVE WORKUP OXIDATIVE WORKUP EXAMPLES O3 Zn / H2O OR O3 1) Pd/H2 • O3 2) H3O+ 2) H2O2 H3O+ + H2O

  20. “At one time” = before spectroscopy. AT ONE TIME OZONOLYSIS WAS WIDELY USED FOR STRUCTURE PROOF BY DEGRADATION Broken apart ( or degraded ) to simpler pieces that are easier to identify. Unknown compound The original structure can be deduced by reassembling the pieces.

  21. oxidative workup WHAT WAS THE ORIGINAL STRUCTURE ? H2O2

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