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Oxidation-Reduction in Organic Chemistry

Oxidation-Reduction in Organic Chemistry. Oxidation of a carbon atom corresponds to an increase in the number of oxygen atoms, and/or bonds to the carbon atom; and/or a decrease in the total number of hydrogen atoms bonded to the carbon atom. . O. C. O. H O. O H. C. H. O H. O. C.

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Oxidation-Reduction in Organic Chemistry

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  1. Oxidation-Reduction in Organic Chemistry Oxidation of a carbon atom corresponds to an increase in the number of oxygen atoms, and/or bonds to the carbonatom; and/or a decrease in the total number of hydrogen atoms bonded to the carbonatom.

  2. O C O HO OH C H OH O C H H H H C H OH C H H H H increasing oxidation state of carbon reducing oxidation state of carbon -4 -2 0 +2 +4

  3. HC CH H H C C H H H H H H C C H H increasing oxidation state of carbon reducing oxidation state of carbon -3 -2 -1

  4. Calculating the oxidation stateof each carbon in a molecule that containscarbons in different oxidation states. CH3CH2OH C2H6O

  5. H H •• C H C O H •• H H Calculating Oxidation Numbers • 1. Write the Lewis structure and include unshared electron pairs.

  6. H H •• H C C O H •• •• •• •• H H •• •• •• •• Calculating Oxidation Numbers • 2. Assign the electrons in a covalent bond between two atoms to the more electronegative partner.

  7. H H •• H C C O H •• •• •• •• H H •• •• •• •• Calculating Oxidation Numbers • 3. For a bond between two atoms of the same element, assign the electrons in the bond equally.

  8. H H •• • • H C C O H •• •• •• •• H H •• •• •• •• Calculating Oxidation Numbers • 3. For a bond between two atoms of the same element, assign the electrons in the bond equally.

  9. H H •• • • H C C O H •• •• •• •• H H •• •• •• •• Calculating Oxidation Numbers • 4. Count the number of electrons assigned to each atom and subtract that number from the number of valence electrons in the neutral atom; the result is the oxidation number. Each H = +1 C of CH3 = -3 C of CH2O = -1 O = -2

  10. Oxidation Numbers • Each of the carbons below have zero formal charge, but they have different oxidation states. • Calculate the oxidation number for each. -4 -2 0 +2 +4

  11. Question Recognizing oxidation and reduction. • Is the conversion from formic acid  carbon dioxide an oxidation or a reduction? • Formaldehyde  methanol? • Acetic acid  acetone • 1) Oxidation 2) Oxidation 3) Oxidation • 1) Oxidation 2) Reduction 3) Oxidation • 1) Reduction 2) Oxidation 3) Reduction • 1) Oxidation 2) Reduction 3) Reduction

  12. C C Generalization Oxidation of carbon occurs when a bond between carbon and an atom which is less electronegative than carbon is replaced by a bond to an atom that is more electronegative than carbon. The reverse process is reduction. oxidation Y X reduction X less electronegative than carbon Y more electronegative than carbon

  13. Oxidation + + HCl CH3Cl Cl2 CH4 Reduction + + CH3Li CH3Cl 2Li LiCl Examples

  14. Question • To carry out the reaction shown below we need: • CH3OH ® H2C=O • A)an oxidizing agent • B)a reducing agent

  15. Fig. 1 Synthesis of alcohols from olefins. G Dong et al. Science 2011;333:1609-1612 Published by AAAS

  16. Fig. 2 Proposed cooperative catalytic system for alcohol synthesis from olefins and water. G Dong et al. Science 2011;333:1609-1612 Published by AAAS

  17. Fig. 3 General reaction scheme for styrene hydration to produce 2-phenylethanol (2a), ethylbenzene (3a), 1-phenylethanol (4a), phenylacetaldehyde (5a), and acetophenone (6a). G Dong et al. Science 2011;333:1609-1612 Published by AAAS

  18. Fig. 4 (A and B) Proposed mechanism and initial mechanistic studies. G Dong et al. Science 2011;333:1609-1612 Published by AAAS

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