Chapter 12 Notes - 12/11/2010 Introduction" Several...

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12/11/2010 1 Chapter 12 Alcohols from Carbonyl Compounds: Oxidation-Reduction and Organometallic Compounds Chapter 12 2 Introduction Several functional groups contain the carbonyl group Carbonyl groups can be converted into alcohols by various reactions Structure of the Carbonyl Group The carbonyl carbon is sp 2 hybridized and is trigonal planar All three atoms attached to the carbonyl group lie in one plane R' N H R O AMIDE Chapter 12 3 The carbonyl group is polarized; there is substantial δ + charge on the carbon The π bond is much weaker than σ bonds – this resonance structure is signiFcant There is about 0.5 + charge on the C of a carbonyl Chapter 12 4 Reactions of Carbonyl Compounds with Nucleophiles Carbonyl groups can undergo nucleophilic addition The nucleophile adds to the δ + carbon The π electrons shift to the oxygen The carbon becomes sp 3 hybridized and therefore tetrahedral Hydride ions and carbanions are two examples of nucleophiles that react with the carbonyl carbon Carbonyl groups and alcohols can be interconverted by oxidation and reduction reactions Alcohols can be oxidized to aldehydes; aldehydes can be reduced to alcohols
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12/11/2010 2 Chapter 12 5 Oxidation-Reduction Reactions in Organic Chemistry Reduction: increasing the hydrogen content and/or decreasing the oxygen content of an organic molecule A general symbol for reduction is [H] Oxidation: increasing the oxygen content and/or decreasing the hydrogen content of an organic molecule A general symbol for oxidation is [O] Oxidation can also be deFned as a reaction that increases the content of any element more electronegative than carbon Chapter 12 6 Oxidation State Based on number of heteroatom (N,O, halogens, etc.) bonds to C CO 2 R X X = Cl, Br, I, etc. SO 2 Me R X X X = Cl, Br, I, etc. SO 2 Me R O O OMe O NH 2 O Chapter 12 7 Alcohols by Reduction of Carbonyl Compounds A variety of carbonyl compounds can be reduced to alcohols Carboxylic acids can be reduced to primary alcohols These are difFcult reductions and require the use of powerful reducing agents such as lithium aluminum hydride (LiAlH 4 also abbreviated LAH) Chapter 12 8 Aldehydes and ketones are reduced to 1 o and 2 o alcohols respectively Aldehydes and ketones are reduced relatively easily; the mild reducing agent
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Chapter 12 Notes - 12/11/2010 Introduction" Several...

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