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Alcohols Biological Activity Nomenclature Preparation Reactions
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Some Alcohols
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Alcohols are Found in Many Natural Products
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Paralytic Shellfish Poisoning
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Ethanol: the Beverage
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Methanol: Not a Beverage
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Oxidation levels of oxygen- halogen- and nitrogen- containing molecules
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Acidity of Alcohols Due to the electronegativity of the O atoms, alcohols are slightly acidic (pKa 16-18). The anion dervived by the deprotonation of an alcohol is the alkoxide. Alcohols also react with Na (or K) as water does to give the alkoxide (red-ox):
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Withdrawing Groups Enhance Acidity alcoholpKa CH 3 OH15.54 CH 3 CH 2 OH16.00 CF 3 CH 2 OH12.43 (CH 3 ) 3 COH18.00 (CF 3 ) 3 COH 5.4
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Phenols are more acidic than alcohols
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Physical Properties CH 3 CH 2 CH 3 -42 0.08 i CH 3 OCH 3 -251.3 ss CH 3 CH 2 OH781.7 vs b.p. o C Dsol. in H 2 O
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Intermolecular H-Bonding
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Alcohol Nomenclature
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Nomenclature
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Preparation of Alcohols Reduction of ketones and aldehydes Reduction of esters and carboxylic acids Hydration of Alkenes Nucleophilic addition –Grignard reaction –Acetylide addition Substitution Epoxide opening
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NaBH 4 Reduction
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Some Examples
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Two Alcohol Products Form in Lab
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LiAlH 4 Reduction a Stronger Reducing Agent
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LiAlH 4 is a much stronger reducing agent
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NaBH 4 is More Selective
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Oxymercuration Hydration Markovnikov
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Hydroboration Hydration Anti-Markovnikov
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Base Catalyzed Ring-Opening of Epoxides
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Acid Catalyzed Ring-Opening Aqueous and in Alcohol
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Nucleophilic addition to Carbonyl Compounds Acetylides
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Organometallic Chemistry Grignard Reaction
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Grignard Reagents React With Ketones to form tertiary alcohols
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Grignard Reagents React With Aldehydes to form secondary alcohols
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Grignard Reagents React With Formaldehyde to form primary alcohols
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Grignard Reagents react (twice) with Esters to form 3 o Alcohols
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Grignard Summary
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Grignard Reagents are exceptionally strong bases
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Synthesis
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Retrosynthetic Analysis
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4-Step Synthesis
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Synthesize Using Only 1,2, or 3-Carbon Reagents
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Retrosynthesis
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Reactions of Alcohols Oxidation R-X, Ether, and Ester Preparation Protection of Alcohols Synthesis The Logic of Mechanisms
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Alcohols are Synthetically Versatile
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Oxidation - Reduction
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Oxidation of 2 o Alcohols with Cr(VI)
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Mechanism
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Oxidation of 1 o Alcohols
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PCC oxidizes 1 o Alcohols to Aldehydes
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Oxidation of 1 o Alcohols to Aldehydes: PCC
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Oxidation Summary
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Reduction Summary
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Conversion of Alcohol into a Leaving Group Form Tosylate (p-TsCl, pyridine) Use strong acid (H 3 O + ) Convert to Alkyl Halide (HX, SOCl 2, PBr 3 )
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Formation of p-Toluenesulfonate Esters
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Best to use p-TsCl with pyridine
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Reactions of Tosylates: Reduction, Substitution, Elimination
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Alcohols to Alkyl Halides
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Lucas Test
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Qualitative test for Alcohol Characterization
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Other Simple Qualitative Tests
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1 o and 2 o Alcohols: best to use SOCl 2, PBr 3, or P/I 2
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Thionyl chloride mechanism in Pyridine – S N 2, Inversion
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Dehydration of Alcohols – E1
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Propose a Mechanism
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Both approaches seem logical
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Take the Blue Route
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Problem Set: Road Map Problem
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Ethers
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Dimerization of Alcohols: Symmetrical Ethers
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Mechanism
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Williamson Ether Synthesis Preparation of Unsymmetrical Ethers
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Mechanism, S N 2
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Alkoxides are strong bases so there is competition with E2 reactions. Bulky alkoxides reacting with primary alkyl halides favor Williamson ether synthesis(S N 2). How would you prepare the following ethers starting from an alcohol and an alkyl halide?
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Alkene Oxides, Oxiranes or Epoxides
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Epoxides are Extremely Reactive
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Cleavage of Unsymmetrical Ethers
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Size 1, Pairwork 8.28 b,d 8.29 a,d 8.33 e,f 8.44 a-e 8.45 8.47 8.51 8.57 8.61 8.64
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