30B-Ch11 - Chapter 11: Ethers Chem 30B Lecture 13, Winter...

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Chapter 11: Ethers Chem 30B Lecture 13, Winter 09
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Structure The functional group of an ether is an oxygen atom bonded to two carbon atoms. In dialkyl ethers, oxygen is sp 3 hybridized with bond angles of approximately 109.5°. In dimethyl ether, the C-O-C bond angle is 110.3°. H H O H C H H H C •• ••
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Structure In other ethers, the ether oxygen is bonded to an sp 2 hybridized carbon. In ethyl vinyl ether, for example, the ether oxygen is bonded to one sp 3 hybridized carbon and one sp 2 hybridized carbon. CH 3 CH 2 -O- CH= CH 2 Ethoxyethene (Ethyl vinyl ether)
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Nomenclature: Ethers IUPAC: the longest carbon chain is the parent. Name the OR group as an alkoxy substituent. Common names: name the groups bonded to oxygen in alphabetical order followed by the word ether ether . 2-Methoxy-2- methylpropane ( tert- Butyl methyl ether) Ethoxyethane (Diethyl ether) CH 3 CH 3 CH 3 CH 2 OCH 2 CH 3 CH 3 OCCH 3 trans- 2-Ethoxy- cyclohexanol OCH 2 CH 3 OH
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Nomenclature: ethers Although cyclic ethers have IUPAC names, their common names are more widely used. IUPAC: prefix ox- ox- shows oxygen in the ring. The suffixes - irane irane , - etane etane , - olane olane , and - ane ane show three, four, five, and six atoms in a saturated ring. Oxirane (Ethylene oxide) Oxolane (Tetrahydrofuran) Oxane (Tetrahydropyran) 1,4-Dioxane O O 1 2 3 O O O O Oxetane
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Physical Properties Although ethers are polar compounds, only weak dipole-dipole attractive forces exist between their molecules in the liquid state.
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Physical Properties Boiling points of ethers are: lower than alcohols of comparable MW. close to those of hydrocarbons of comparable MW Ethers are hydrogen bond acceptors. They are more soluble in H 2 O than hydrocarbons.
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Preparation of Ethers Williamson ether synthesis: Williamson ether synthesis: Ether synthesis by the S N 2 displacement of halide, tosylate, or mesylate by alkoxide ion. 2-Methoxypropane (Isopropyl methyl ether) Iodomethane (Methyl iodide) Sodium isopropoxide + + CH 3 CH 3 CH 3 I CH 3 CHO - Na + CH 3 CHOCH 3 Na + I - S N 2
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Preparation of Ethers Yields are highest with methyl and 1° halides, lower with 2° halides (competing β -elimination) reaction fails with 3° halides ( β -elimination only). CH 3 CH 3 CH 3 CO K + CH 3 Br S N 2 CH 3 CH 3 CH 3 COCH 3 K + Br - + + Potassium tert- butoxide Bromomethane (Methyl bromide) 2-Methoxy-2-methylpropane ( tert- Butyl methyl ether) CH 3 CH 3 CH 3 CBr CH 3 O - Na + E2 CH 3 CH 3 C=CH 2 CH 3 OH Na + Br - + + + 2-Bromo-2- methylpropane Sodium methoxide 2-Methylpropene
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Preparation of Ethers Acid-catalyzed dehydration of alcohols Diethyl ether and several other ethers are made this way on an industrial scale. – A specific example of an S
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This note was uploaded on 04/29/2009 for the course CHEM CHEM 30B taught by Professor Maynard during the Winter '08 term at UCLA.

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30B-Ch11 - Chapter 11: Ethers Chem 30B Lecture 13, Winter...

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