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BU CHEM 102 - Structural Characteristics of Ethers
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Chem 102 1st Edition Lecture 11Outline of Last Lecture I. Chapter 14: 3.14-3.19 Chemical Reactions of Alcohols, Structural Characteristics of Phenols, Nomenclature for Phenols, Physical and Chemical Properties of Phenols, Occurrence and Uses of PhenolsOutline of Current Lecture II. 3.14 - Structural Characteristics of EthersIII. 3.15 - Nomenclature of EthersIV. 3.16 - Isomerism for EthersV. 3.17 - Physical and Chemical Properties of EthersVI. 3.18 - Cyclic EthersVII. 3.19 - Sulfur Analogs of Alcohols and EthersCurrent Lecture3.14 - Structural Characteristics of Ethers- Ethers: Oxygen bonded to two carbon atoms (functional group) - General formula: R-O-R – Examples: - CH3-O-CH3, CH3-O-C2H5 - Water and ether have similar structure in that two H atoms of water are replaced by R groups in ethers 3.15 - Nomenclature of EthersCommon Names • Name the two hydrocarbon groups attached to oxygen atom of the ether and add the word ether - The hydrocarbon groups are listed in alphabetical order - When both R groups are same than di is used with the name of R group – Examples: IUPAC Nomenclature • Rule 1: Select the longest carbon chain and use its name as the base name. • Rule 2: Change the “-yl” ending of the other hydrocarbon group to “-oxy” to obtain the alkoxy group name − Examples: methyl becomes methoxy, ethyl becomes ethoxy, etc.• Rule 3: Place the alkoxy name, with a locant number, in front of the base chain name. 3.16 - Isomerism for Ethers• Ethers have carbon chains (two alkyl groups ) therefore the constitutional isomerism possibilities in ethers depend on: 1. The partitioning of carbon atoms between the two alkyl groups, and…. 2. Isomerism possibilities for the individual alkyl groups present. • Isomerism is not possible for a C2 or a C3 ethers • C4 and C5 ethers exhibit constitutional isomers. Functional Group Isomerism (new type!) • Ethers and alcohols with the same number of carbon atoms and the same degree of saturation have the same molecular formula. − For example: Dimethyl ether, and ethyl alcohol both have the molecular formula C2H6O (constitutional isomers). • Functional group isomers are constitutional isomers that contain different functional groups. − C3 ether–alcohol functional group isomerism possibilities are three o Ethyl methyl ethero Propyl alcoholo Isopropyl alcohol3.17 - Physical and Chemical Properties of EthersPhysical properties • The boiling points of ethers are similar to those of alkanes of comparable molecular mass and are much lower than those of alcohols of comparable molecular mass. • Ethers more soluble in water than alkanes of similar molar mass because ethers can form hydrogen bonds. Chemical properties • Ethers are Flammable, e.g., Diethyl ether has boiling point of 35oC and therefore a flash-fire hazard. • Ethers react slowly with oxygen from the air to form unstable hydroperoxides and peroxides.• Unreactive towards acids, bases and oxidizing agents (makes them useful solvents for organic reactions) • Like alkanes, ethers also undergo halogenation reactions 3.18 - Cyclic Ethers• Cyclic ethers: Contain the ether functional groups as part of a ring system (heterocyclic organic compounds). • Heterocyclic organic compound: a cyclic organic compound in which one or more of the carbon atoms in the ring have been replaced with atoms of other elements. • Important cyclic ethers: o Tetrahydrofuran (THF) : Useful as a solvent in that it dissolves many organic compounds and yet is miscible with water. o Polyhydroxy derivatives of the five-membered (furan) and six membered (pyran) carbohydrates are cyclic ether systems 3.19 - Sulfur Analogs of Alcohols and Ethers• R-SH ---- Thiol • R-S-R ---- Thioether • Lower boiling point than corresponding alcohols due to lack of hydrogen bonding • Strong disagreeable odor - Natural gas odor is due to added thiols • Thiols are named in the same way as alcohols in the IUPAC system, except that the “–ol” becomes “-thiol. ” • The prefix thio- indicates the substitution of a sulfur atom for an oxygen atom. • As in the case of diols and triols, the “-e” at the end of the alkane name is also retained for thiols. Properties of Thiols • Have lower boiling points than alcohols (weak hydrogen bonding) • Have strong, disagreeable odor- The familiar odor of natural gas results from the addition of a low concentration of methanethiol(CH3—SH) to the gas. – The scent of skunks is due to two thiols. • Oxidation of thiols: Lead to disulfide (S-S) bond formation 2 R-SH <- ->R-S-S-R + 2H • The above reaction is of biological importance - Disulfide bonds formed from two —SH groups aid in protein structure stabilization • Thioethers (or sulfides): An organic compound in which a sulfur atom is bonded to two carbon atoms by single bonds. • General formula: R—S—R. • Like thiols, thioethers (or sulfides) have strong characteristic odors. • Thiols and thioethers exhibit functional group isomerism in the same manner that alcohols and ethers.Exam I, Thursday, 7:00pmChapters- 12- 13- 14Recommended Materials to study for the exam- Lecture Notes- Textbook- End of chapter problems (in textbook)- Quizzes- Discussion Practice Problem Packets- OWL (online practice problems) - If needed make a tutoring appointment with the UTS they are very helpful- Office hours with TA and/or


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