Ethers

Nomenclature Nomenclature of Alcohols (Sec. 4.3F) Nomenclature of Ethers Common Names The groups attached to the oxygen are listed in alphabetical order IUPAC Ethers are named as having an alkoxyl substituent on the main chain Chapter 11

Chapter 11 Cyclic ethers can be named using the prefix oxa- Three-membered ring ethers can be called oxiranes; Four-membered ring ethers can be called oxetanes Chapter 11

Synthesis of Ethers Ethers by Intermolecular Dehydration of Alcohol Primary alcohols can dehydrate to ethers This reaction occurs at lower temperature than the competing dehydration to an alkene This method generally does not work with secondary or tertiary alcohols because elimination competes strongly The mechanism is an SN2 reaction Chapter 11

Reactions of Ethers Acyclic ethers are generally unreactive, except for cleavage by very strong acids to form the corresponding alkyl halides Dialkyl ethers undergo SN2 reaction to form 2 equivalents of the alkyl bromide Chapter 11

Epoxides Epoxides are three-membered ring cyclic ethers These groups are also called oxiranes Epoxides are usually formed by reaction of alkenes with peroxy acids This process is called epoxidation and involves syn addition of oxygen Chapter 11

Reactions of Grignard Reagents with Oxiranes (Epoxides) Grignard reagents are very powerful nucleophiles and can react with the d+ carbons of oxiranes The reaction results in ring opening and formation of an alcohol product Reaction occurs at the least-substituted ring carbon of the oxirane The net result is carbon-carbon bond formation two carbons away from the alcohol Chapter 12

Chapter 12

Introduction The polarity of a carbon-halogen bond leads to the carbon having a partial positive charge In alkyl halides this polarity causes the carbon to become activated to substitution reactions with nucleophiles Carbon-halogen bonds get less polar, longer and weaker in going from fluorine to iodine Chapter 6

Nucleophilic Substitution Reactions In this reaction a nucleophile is a species with an unshared electron pair which reacts with an electron deficient carbon A leaving group is substituted by a nucleophile Examples of nucleophilic substitution Chapter 6

Organic Synthesis: Functional Group Transformations Using SN2 Reactions Stereochemistry can be controlled in SN2 reactions Chapter 6