tailieunhanh - Ebook Organic chemistry (7e): Part 2

The book updated material on Infrared Spectroscopy and Nuclear Magnetic Resonance of amines, aldehydes/ketones, and carboxylic acid derivatives. Updated information on DNA sequencing (the process of determination of the precise sequence of nucleotides within a DNA molecule) and DNA synthesis. | Chapter 18 - Ethers and Epoxides Thiols and Sulfides Chapter Outline I. Acyclic ethers Sections - A. Naming ethers Section . 1. Ethers with no other functional groups are named by citing the two organic substituents and adding the word ether . 2. When other functional groups are present the ether is an alkoxy substituent. B. Properties of ethers. 1. Ethers have the same geometry as water and alcohols. 2. Ethers have a small dipole moment that causes a slight boiling point elevation. 3. Ethers can react slowly with oxygen to give explosive peroxides. c. Preparation of ethers Section . 1. Symmetrical ethers can be synthesized by acid-catalyzed dehydration of alcohols. 2. Williamson ether synthesis. a. Metal alkoxides react with primary alkyl halides and tosylates to form ethers. b. The alkoxides are prepared by reacting an alcohol with a strong base such as NaH. Reaction of the free alcohol with the halide can be achieved with Ag2O. c. The reaction occurs via an Sn2 mechanism. i. The halide component must be primary. ii. In cases where one ether component is hindered reaction should occur between the alkoxide of the more hindered reagent and the halide of the less hindered reagent. 3. Alkoxymercuration of alkenes. a. Ethers can be formed from the reaction of alcohols with alkenes. b. The reaction is catalyzed by mercuric trifluoroacetate. c. The mechanism is similar to that for hydration of alkenes. NaBH4 is used for demercuration of the intermediate. d. Many different types of ethers can be prepared by this method. D. Reactions of ethers Sections - . 1. Acidic cleavage Section . a. Strong acids can be used to cleave ethers. b. Cleavage can occur by Sn2 or SnI routes. i. Primary and secondary alcohols react by an Sn2 mechanism in which the halide attacks the ether at the less hindered site. This route selectively produces one halide and one alcohol. ii. Tertiary benzylic and allylic ethers react by either an SnI or an El route. 2. .