lecture 11 - Structure Ethers & Epoxides Chapter 11 The...

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Ethers & Ethers & Epoxides Epoxides Chapter 11 Chapter 11 Structure 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° 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 2 -O-CH=CH 2 Ethoxyethene (Ethyl vinyl ether) Nomenclature: ethers 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 (used mostly for low -molecular weight ethers) molecular weight ethers) 2-Methoxy-2- methylpropane ( tert- Butyl methyl ether) Ethoxyethane (Diethyl ether) (trans- 2-Ethoxy- cyclohexanol) (1R,2R-2-Ethoxycyclohexanol 2-Methoxyethanol 2-Ethoxyethanol More Examples Nomenclature: ethers Nomenclature: ethers (heterocycles heterocycles ) ± Although cyclic ethers have IUPAC names, their common names are more widely used IUPAC: prefix ox - shows oxygen in the ring the suffixes - irane , - etane etane , - olane olane , and - ane ane show three, four, five, and six atoms in a saturated ring
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Nomenclature Examples Nomenclature Examples Cyclohexoxycyclohexane Methoxyethene or Methyl vinyl ether Nomenclature Practice Nomenclature Practice Physical Properties ± Although ethers are polar compounds, only weak dipole-dipole attractive forces exist between their molecules in the pure liquid state Physical Properties 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 are hydrocarbons Boiling Points and Solubilities in Water of Some Ethers and Alcohols of Comparable Molecular Weight Preparation of Ethers Preparation of Ethers ± Williamson ether synthesis: Williamson ether synthesis: S N 2 displacement of halide, by alkoxide ion
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Preparation of Ethers Preparation of Ethers yields are highest with methyl and 1° halides, lower with 2° halides (competing β -elimination) Preparation of Ethers Preparation of Ethers reaction fails with 3° halides ( β -elimination only) Preparation of Ethers ± Acid-catalyzed dehydration of alcohols diethyl ether and several other ethers are made on an industrial scale this way a specific example of an S N 2 reaction in which a poor leaving group (OH - ) is converted to a better one (H 2 O) Mech: Acid-catalyzed dehydration of alcohols Step 1: proton transfer gives an oxonium ion Use H 3 O + instead of H 2 SO 4 Mech: Acid-catalyzed dehydration of alcohols Step 2: nucleophilic displacement of H 2 O by the OH group of the alcohol gives a new oxonium ion Mech: Acid-catalyzed dehydration of alcohols Step 3: proton transfer to solvent completes the reaction
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This note was uploaded on 09/06/2009 for the course CHEM chem 12 AB taught by Professor Valentin during the Spring '09 term at Evergreen Valley.

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lecture 11 - Structure Ethers & Epoxides Chapter 11 The...

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