Chapter 9 Reactions of Alcohols, Ethers, Epoxides, Amines, and Thiols PDF

Chapter 9 Reactions of Alcohols, Ethers, Epoxides, Amines, and Thiols Fundamentals of Organic Chemistry CHEM 209 Dr. Kifah Salih © 2017 Pearson Education, Ltd.  9.1 The Nomenclature...

Chapter 9 Reactions of Alcohols, Ethers, Epoxides, Amines, and Thiols Fundamentals of Organic Chemistry CHEM 209 Dr. Kifah Salih © 2017 Pearson Education, Ltd.  9.1 The Nomenclature of Alcohols Common Names of Alcohols Systematic Names of Alcohols The OH is the “functional group.” The systematic nomenclature uses a suffix to denote a functional group. Alcohols are named by replacing the “e” at the end of the parent hydrocarbon with the suffix “ol.” The parent hydrocarbon is the longest chain that contains the functional group. Number the chain in the direction that gives the functional group the lowest possible number. © 2017 Pearson Education, Ltd.  Systematic Names of Alcohols © 2017 Pearson Education, Ltd.  Compounds with Two OH Groups When there is both a functional group and a substituent, the functional group gets the lowest number. © 2017 Pearson Education, Ltd.  Nomenclature of Alcohols © 2017 Pearson Education, Ltd.  9.2 Activating an Alcohol for Nucleophilic Substitution by Protonation Alcohols must be “activated” before they can react. Only weakly basic nucleophiles can be used. Strongly basic nucleophiles will react with the proton. © 2017 Pearson Education, Ltd.  Converting Alcohols into Alkyl Halides Primary and secondary alcohols require heat; tertiary alcohols do not. © 2017 Pearson Education, Ltd.  The Reactions of Secondary and Tertiary Alcohols with Hydrogen Halides are SN1 Reactions Tertiary Alcohol © 2017 Pearson Education, Ltd.  The Reactions of Primary Alcohols with Hydrogen Halides are SN2 Reactions Primary Alcohol Recall that Br− is a good nucleophile in a protic solvent. Alcohols undergo SN1 reactions unless they would have to form a primary carbocation. The rate of dehydration depends on the ease of carbocation formation. © 2017 Pearson Education, Ltd.  9.4 Elimination Reactions of Alcohols: Dehydration Dehydration of an alcohol is an elimination reaction. To prevent the alkene from adding water and reforming the alcohol, the water is removed as it is formed. Dehydration of Secondary and Tertiary Alcohols are E1 Reactions © 2017 Pearson Education, Ltd.  Dehydration is a Regioselective Reaction The major product is the more stable alkene. The More Stable Alkene Has the More Stable Transition State Leading to Its Formation © 2017 Pearson Education, Ltd.  E2 Dehydration of Primary Alcohols Both E2 and SN2 products are obtained. Dehydration is an E1 reaction unless a primary carbocation must be formed—then it is E2. Dehydration is Stereoselective The major product is the stereoisomer with the largest groups on opposite sides of the double bond. © 2017 Pearson Education, Ltd.  9.5 Oxidation of Alcohols Secondary Alcohols Primary Alcohols To stop at the aldehyde Tertiary alcohols cannot be oxidized to a carbonyl compound © 2017 Pearson Education, Ltd.  Oxidation by hypochlorous acid (HOCl) The Mechanism © 2017 Pearson Education, Ltd.  9.6 Nomenclature of Ethers © 2017 Pearson Education, Ltd.  9.7 Nucleophilic Substitution Reactions of Ethers Alcohols and ethers must be “activated” before the compounds can react. Reagents such a SOCl2, PCl3, and TosCl cannot be used to activate ethers because ethers do not have a proton that must be lost to form a stable product. © 2017 Pearson Education, Ltd.  Mechanism for Ether Cleavage: SN1 SN1 If a relatively stable carbocation is formed when ROH leaves, it will be an SN1 rxn. SN2 If a relatively stable carbocation is not formed when ROH leaves, it will be an SN2 reaction. © 2017 Pearson Education, Ltd.  9.8 Nucleophilic Substitution Reactions of Epoxides An epoxide can be named as an alkane, with an “epoxy” prefix that identifies the carbons to which the oxygen is attached. © 2017 Pearson Education, Ltd.  Epoxides are More Reactive Than Ethers Because of Ring Strain An epoxide is formed from the reaction of an alkene with a peroxyacid (RCO3H, such as t-BuCO3H, CH3CO3H, mCPBA. It is this oxygen that is transferred to the alkene in order to from the epoxide. Epoxides are much more reactive than ethers in nucleophilic substitution reactions because of the ring strain. © 2017 Pearson Education, Ltd.  Nucleophilic Substitution: Acidic Condition Epoxides are more reactive than ethers, so the reaction easily occurs at room temperature. © 2017 Pearson Education, Ltd.  Nucleophile Substitution Acidic Conditions Under acidic conditions, the nucleophile preferentially attacks the more substituted ring carbon. © 2017 Pearson Education, Ltd.  Nucleophilic Substitution: Neutral or Basic Conditions Under neutral or basic conditions, the nucleophile preferentially attacks the less sterically hindered ring carbon. © 2017 Pearson Education, Ltd.  Using Epoxides in Synthesis Epoxides are useful reagents because they can react with a wide variety of nucleophiles, leading to the formation of a wide variety of products. © 2017 Pearson Education, Ltd.  Extra Examples © 2017 Pearson Education, Ltd.  9.11 Nomenclature of Thiols Thiols (pKa ~ 10) are stronger acids than alcohols (pKa ~ 15). Thiols have lower boiling points than alcohols. ethanethiol ethanol 37 °C 78 °C Thiolate ions are better nucleophiles than alkoxide ions in a protic solvent. The product is a sulfur analogue of an ether (a thioether or a disulfide). © 2017 Pearson Education, Ltd.