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More About the Families in Group II The families in Group II all have an electronegative atom or group that is attached to an sp3 carbon. © 2014 Pearson Education, Inc. כוהלים ואתרים-5 1 Strongly Basic Leaving Groups Cannot Be Displaced כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 2 Acid Converts the Poor Leaving Group into a Good Leaving Group Alcohols have to be “activated” before they can react. Only weakly basic nucleophiles can be used. Strongly basic nucleophiles would react with the proton. כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 3 Converting Alcohols to Alkyl Halides Primary and Secondary alcohols require heat; tertiary alcohols do not. © 2014 Pearson Education, Inc. כוהלים ואתרים-5 4 The Reactions of Secondary and Tertiary Alcohols with Hydrogen Halides are SN1 Reactions כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 5 An SN1 Reaction Creates a Carbocation Intermediate, So Watch Out for Carbocation Rearrangements כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 6 Ring Expansion כוהלים ואתרים-5 7 © 2011 Pearson Education, Inc. The Reactions of Primary Alcohols with Hydrogen Halides are SN2 Reactions Recall that Br– is a good nucleophile in a protic solvent. Alcohols undergo SN1 reactions unless they would have to form a primary carbocation. © 2014 Pearson Education, Inc. כוהלים ואתרים-5 8 Cl– is the Poorest Nucleophile of the Halide Ions ZnCl2 increases the rate of the reaction by creating a better leaving group than water. רשות כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 9 Why is It Important to Be Able to Convert Alcohols to Alkyl Halides? Alcohols are readily available but unreactive. Alkyl halides are less available but reactive and can be used to synthesized a wide variety of compounds. © 2014 Pearson Education, Inc. כוהלים ואתרים-5 10 Other Methods to Convert Alcohols into Alkyl Halides phosphorus tribromide, phosphorus trichloride, thionyl chloride כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 11 The Mechanism for the Reaction with PBr3 or PCl3 רשות A bromophosphite (chlorophosphite) group is a better leaving group than a halide ion. Pyridine is the solvent and acts as a base. © 2014 Pearson Education, Inc. כוהלים ואתרים-5 12 The Mechanism for the Reaction with SOCl2 רשות A chlorosulfite group is a better leaving group than a halide ion. Pyridine is the solvent and acts as a base. © 2014 Pearson Education, Inc. כוהלים ואתרים-5 13 Converting Alcohols to Alkyl Halides כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 14 Primary and Secondary Alcohols Can Be Activated by Being Converted to Sulfonate Esters כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 15 A Sulfonic Acid is a Strong Acid כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 16 Common Sulfonyl Chlorides tosyl chloride = TsCl כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 17 The Mechanism רשות כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 18 A Sulfonate Ester Reacts with Nucleophiles כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 19 Dehydration of an Alcohol Dehydration of an alcohol is an elimination reaction. כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 20 Dehydration is a Reversible Reaction To prevent the alkene from adding water and reforming the alcohol, the water is removed as it is formed. כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 21 Dehydration of Secondary and Tertiary Alcohols are E1 Reactions כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 22 Dehydration The major product is the more stable alkene. כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 23 The More Stable Alkene Has the More Stable Transition State Leading to Its Formation כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 24 Tertiary Alcohols are the Easiest to Dehydrate The rate of dehydration reflects the ease of carbocation formation. כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 25 An E1 Reaction Creates a Carbocation Intermediate, So Watch Out for Carbocation Rearrangements כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 26 Dehydration of a Primary Alcohol is an E2 Reaction Both E2 and SN2 products are obtained. Alcohols undergo E1 reactions unless they would have to form a primary carbocation. © 2014 Pearson Education, Inc. כוהלים ואתרים-5 27 Dehydration The major product is the stereoisomer with the largest groups on opposite sides of the double bond. כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 28 Oxidation of Secondary Alcohols כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 29 Oxidation of Primary Alcohols כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 30 Tertiary Alcohols Cannot Be Oxidized to a Carbonyl Compound כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 31 Oxidation by Hypochlorous Acid (HOCl) כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 32 The Mechanism רשות כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 33 Alcohols and Ethers Have Similar Leaving Groups Alcohols and ethers have to be “activated” before the compounds can react. כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 34 The Leaving Group of an Ether Can Be Activated by Protonation כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 35 The Mechanism If a relatively stable carbocation is formed when ROH leaves, it will be an SN1 reaction. כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 36 The Mechanism If a relatively stable carbocation would not be formed when ROH leaves, it will be an SN2 reaction. Ethers undergo SN1 reactions unless they would have to form a primary carbocation. כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 37 Nomenclature of Epoxides אלקנים-6 © 2014 Pearson Education, Inc. 38 Epoxides are More Reactive Than Ethers Because of Ring Strain כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 39 The Acid-Catalyzed Mechanism כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 40 If the Epoxide is Not Symmetrical, Which Carbon Does the Nucleophile Attack? The nucleophile attacks the more substituted ring carbon. כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 41 Under Acidic Conditions the Nucleophile Attacks the More Substituted Ring Carbon כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 42 Under Neutral or Basic Conditions the Nucleophile Attacks the Less Substituted Carbon כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 43 The Conditions Determine the Site of Nucleophilic Attack כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 44 Using Epoxides in Synthesis כוהלים ואתרים-5 © 2014 Pearson Education, Inc. 45 ריאגנט גריניאר Grignard Reagents: Alkylmagnesium halide, RMgX, produced from reaction of alkyl halides, RX, with magnesium metal in ether or tetrahydrofuran (THF) solvent The carbon atom is both nucleophilic and basic 46 כוהלים ואתרים-5 ריאגנט גריניאר They react with weak acids such as H2O, ROH, RCO2H, and RNH2 to abstract a proton and yield hydrocarbons Since hydrocarbons are weak acids, with pKa’s in the range of 44 to 60, carbon anions are very strong bases Because even trace amounts of moisture can destroy an organometallic compound, it is important that all reagents be dry when organometallic compounds are being synthesized and when they react with other reagents 47 כוהלים ואתרים-5 מחמצנים ומחזרים ביולוגיים -5כוהלים ואתרים 48 מנגנון [רשות] -5כוהלים ואתרים 49 ] [העשרהAn Unusual Antibiotic 50 כוהלים ואתרים-5