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18.S: Ethers and Epoxides; Thiols and Sulfides (Summary)

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    Concepts & Vocabulary

    18.0 Introduction

    • Ethers are molecules containing oxygen which is bonded to two carbon groups.
    • Thiols are sulfur analogues of alcohols with an SH group instead of OH.
    • Sulfides are sulfur analogues of ethers with sulfur bonded to two carbon groups instead of oxygen.

    18.1 Names and Properties of Ethers

    • Ether groups are named as alkoxy groups.
    • Ethers do not have intramolecular hydrogen bonding (unlike alcohols), therefore ethers have significantly reduced intermolecular forces causing boiling points that are much lower than similar sized alcohols.

    18.2 Preparing Ethers

    • Alkoxymercuration can be used to prepare an ether from an alkene.

    18.3 Reactions of Ethers: Acidic Cleavage

    • The carbon-oxygen bonds of ethers can be cleaved with strong acids through either nucleophilic substitution or elimination reactions.

    18.4 Reactions of Ethers: Claisen Rearrangement

    • The Claisen rearrangement is a [3, 3] sigmatropic rearrangement reaction that converts aryl or enol ethers into carbonyl compounds (though the aromatic version rearranges into a phenol to re-establish aromaticity.

    18.5 Cyclic Ethers: Epoxides

    • Epoxides, also called oxiranes, have a three-membered ring structure with one oxygen and two carbon atoms.
    • Epoxides can be formed from alkenes by reaction with peroxy acids (MCPBA for example).
    • Epoxides can be formed from halohydrin molecules by reaction with a base, which causes an intramolecular Williamson ether synthesis.

    18.6 Reactions of Epoxides: Ring Opening

    • When epoxides are ring opened under basic conditions, they follow SN2 mechanism leading to the nucleophile adding to the less substituted side of the epoxide.
    • When epoxides are ring opened under acidic conditions, they follow SN1 mechanism leading to the nucleophile adding to the more substituted side of the epoxide.
    • When epoxides are ring opened in aqueous reactions, the result is an anti-diol.
    • Halo acids can be added to epoxides to form anti-halohydrins.

    18.7 Crown Ethers

    • Crown ethers are cyclic ethers containing several oxygen atoms.
    • Crown ethers are named by the number of total atoms in the ring, followed by the word crown and finally the number of oxygen atoms (18-crown-6 for example).

    18.8 Thiols and Sulfides

    • Thiols can be prepared from alkyl halides through reaction with hydrosulfide ion (SH-) or through a more complicated series of reactions including thiourea.
    • Thiols can be oxidized with mild oxidizing agents to form disulfides.
    • Disulfide bridges link cysteine residues in protein structures.
    • Sulfides are sulfur analogues of ether, though are much better nucleophiles with sulfur in place of oxygen.

    18.9 Spectroscopy of Ethers

    • Ethers show standard C-H stretches and bends in IR along with a strong C-O stretch around 1000 cm-1.
    • In 1H NMR, hydrogens on carbons adjacent to the oxygen typically appear between 3.4-4.5 ppm.
    • Hydrogens on carbons of an epoxide ring typically appear between 2.5-3.5 ppm in 1H NMR.

    18.10 Interchapter: A Preview of Carbonyl Chemistry

    • Carbonyl groups are one of the most important features in organic chemistry and consist of a sp2 carbon double-bonded to oxygen.
    • Carbonyl groups are present in ~10 different functional groups.
    • Carbonyl groups are polarized with a partial positive charge on carbon and partial negative charge on oxygen. This makes the carbon atom an electrophile, while the oxygen can act as a nucleophile.
    • Carbonyl groups can react through several mechanisms including nucleophilic addition and nucleophilic acyl substitution, alpha substitution and condensation.

    Skills to Master

    • Skill 18.1 Name ethers using common naming and IUPAC.
    • Skill 18.2 Write reaction equations for preparation of ethers.
    • Skill 18.3 Write mechanisms for reactions of ethers with strong halogen acids.
    • Skill 18.4 Draw mechanisms for Cope and Claisen rearrangements.
    • Skill 18.5 Draw mechanisms for ring-opening epoxides under acidic and basic conditions.
    • Skill 18.6 Draw and name crown ethers.
    • Skill 18.7 Explain how disulfide bridges contribute to protein structure.
    • Skill 18.8 Give an example of S-adenosyl methionine activity in biological systems.
    • Skill 18.9 Use IR and NMR spectra to identify ethers.

    Summary of Reactions

    Ether and Epoxide Preparation

    Ether Reactions

    Epoxide Reactions

    Sulfur Compound Reactions

    18.S: Ethers and Epoxides; Thiols and Sulfides (Summary) is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

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