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Naming Ethers • Common names are used frequently: 1. Name each –R group. 2. Arrange them alphabetically. 3. End with the word “ether.” Naming Ethers • IUPAC systematic names are often used as well: 1. Make the larger of the –R groups the parent chain. 2. Name the smaller of the –R groups as an alkoxy substituent. • SEE: SKILLBUILDER 14.1. Crown Ethers K+ K+ K+ Question • Which reaction is the best candidate for catalysis by 18 -crown-6? (Which reaction proceeds faster in the presence of the crown ether than in its absence?) • • • • A) B) C) D) K+ Bromobutane + KCN (in toluene) Phenol + Br2 (in water) Butanol + H2CrO4 (in water) CH3CH2CH2CHO + H2 (in ethanol) Na+ Li+ Question • What is the name of the crown ether show at the right? • A) 12-crown-4 • B) 10-crown-5 • C) 15-crown-5 • D) 18-crown-6 Question • Which crown ether would provide the fastest rate for the following reaction? • • • • A) B) C) D) 12-crown-4 10-crown-5 15-crown-5 18-crown-6 Question What is the product of the following reaction? Question What is the correct order of reagents needed for the following transformation? Mechanism Question • Which of the following best represents the rate-determining transition state for the reaction shown below? • A) • C) B) D) Question • The most effective pair of reagents for the preparation of tert -butyl ethyl ether is • A) potassium tert-butoxide and ethyl bromide. • B) potassium tert-butoxide and ethanol. • C) sodium ethoxide and tert-butyl bromide. • D) tert-butyl alcohol and ethyl bromide Limitation Preparation of Epoxides w/ peroxyacids (MCPBA) . Question Which of the following will produce the epoxide below? Epoxidation Stereochemistry • Epoxidation forms a racemic mixture because reaction occurs with equal probability on either face of the double bond. Enantioselective Epoxidation • The desired epoxide can be formed in excess by choosing the appropriate catalyst. Note the position of the –OH group. • SEE: CONCEPTUAL CHECKPOINT 14.16. Enantioselective Epoxidation • In order to have an optically active product, one of the reactants, or reagents, or catalyst in a reaction must be chiral. • An example is a Sharpless catalyst, which forms such a chiral complex that favors the formation of one enantiomeric epoxide versus the other. • Catalyst: Question What is the product of the following reaction? Question True (A) / False (B) Ring-opening of Epoxides • Epoxides can be opened by many strong nucleophiles. • Both regioselectivity and stereoselectivity must be considered. Ring-opening of Epoxides Question • What is the product isolated when the epoxide below reacts with NaOCH3 in CH3OH? • A) B) • C) D) Question • What is the product of the reaction shown? • A) B) • C) D) Question What are the product(s) of the following reaction? Acid-Catalyzed Ring-Opening Reactions of Epoxides Question • What is the product isolated when the epoxide at the right reacts with CH3OH and H2SO4? • A) • C) B) D) Question What is the product of the following reaction? Thiols & Thio Ethers Thiols • Sulfur appears just under oxygen on the periodic table. • Sulfur appears in THIOLS as an –SH group analogous to the –OH group in alcohols. Thiols / Mercaptans • Thiols are also known as mercaptans. • The –SH group can also be named as part of a side group rather than as part of the parent chain. • The mercaptan name comes from their ability to complex mercury. • 2,3-dimercapto-1-propanol is used to treat mercury poisoning. Thiols / Mercaptans Thioethers / Sulfides • Thiols are known for their unpleasant odor. • Skunks use thiols as a defense mechanism: (E)-2butene-1-thiol, 3-methyl-1-butanethiol, and 2quinolinemethanethiol, and acetate thioesters of these. • Methanethiol is added to natural gas (methane) so that gas leaks can be detected. • The hydrosulfide ion (HS–) is a strong nucleophile and a weak base. • HS– promotes SN2 rather than E2. • Sulfur analogs of ethers are called SULFIDES or THIOETHERS. • Sulfides can also be named as a side group. Question Thioethers / Sulfides • Sulfides are generally prepared by nucleophilic attack of a thiolate on an alkyl halide. Thioethers / Sulfides Sulfide reactions: What is the correct order of reagents needed for the following transformation? Thioethers / Sulfides Sulfide reactions: Nucleophilic substitution of an alkyl halide: Nucleophilic substitution of an alkyl halide: The process produces a strong alkylating reagent that can add an methyl group to a variety of nucleophiles such as genetic bases and histones, as noted in the Epigenetics bonus Webinar The process produces a strong alkylating reagent that can add an methyl group to a variety of nucleophiles such as genetic bases and histones, as noted in the Epigenetics bonus Webinar Thioethers / Sulfides Thioethers / Sulfides Methylation of cytosine, a genetic base: Nucleophilic substitution of SAM-CH3 (SAM = S-adenosylmethionine) Where cytosine is the nucleophile. Sulfide reactions: Oxidation: sodium meta-periodate produces a sulfoxide. Thioethers / Sulfides Consider the IR of dimethylsulfoxide (DMSO) and the resonance structures below it. An S=O bond has a strong peak @ ~1050 cm-1 and an S-O bond @ 700-900 cm-1. Which resonance form should predominate? Question What is the correct order of reagents needed for the following transformation? Thioethers / Sulfides Sulfide reactions: Oxidation: hydrogen peroxide produces a sulfone.