Chapter 14 – Ethers, Epoxides, Thioethers, and Silyl Ethers

Vocabulary flashcards covering core terms, reactions, solvents, and mechanistic concepts from Chapter 14 on ethers, epoxides, thioethers, and silyl ethers.

Ether

An R–O–R′ compound in which oxygen is bonded to two carbon atoms; lacks O–H bond and cannot hydrogen-bond as a donor.

Symmetrical ether

An ether whose two alkyl (or aryl) groups are identical, e.g., diethyl ether.

Unsymmetrical ether

An ether whose two substituents differ, e.g., methyl phenyl ether (anisole).

Epoxide (oxirane)

A three-membered cyclic ether with significant ring strain; formula C2H4O.

Furan

An aromatic five-membered heterocycle (C4H4O) with one oxygen; parent of the ‘oxole’ series.

Tetrahydrofuran (THF)

A saturated five-membered cyclic ether (C4H8O); common polar aprotic solvent, bp 65 °C. (no hydrogen bonding)

1,4-Dioxane

A six-membered ring containing two opposite oxygens; higher-boiling (bp 101 °C) polar aprotic solvent.

1,2-Dimethoxyethane (DME, glyme)

Linear diether (CH3OCH2CH2OCH3); polar aprotic solvent able to solvate cations.

Diethyl ether

Classic laboratory solvent (bp 35 °C) that solvates cations well but cannot donate H-bonds.

Polar aprotic solvent

Medium with significant dipole moment but no acidic hydrogens; stabilises cations, e.g., ethers.

Crown ether

Macrocyclic polyether that wraps around metal cations via lone-pair donation (e.g., 18-crown-6 for K⁺).

Williamson Ether Synthesis

SN2 reaction between an alkoxide (RO–) and a 1° alkyl halide or tosylate to form R–O–R′.

Phenoxide alkylation

Using a deprotonated phenol in Williamson synthesis; works only with aliphatic halides (no SN2 on aryl).

Alkoxymercuration–demercuration

Addition of ROH + Hg(OAc)₂ across an alkene followed by NaBH₄ to give Markovnikov ethers without rearrangement.

Acid-catalyzed condensation of alcohols

Bimolecular dehydration (H₂SO₄, 140 °C) of two 1° alcohols to form symmetrical ethers + water.

Cleavage of ethers by HBr/HI

Strong HX converts R–O–R′ into alkyl halides via protonation and SN1/SN2 pathways.

Thioether (sulfide)

Sulfur analogue of an ether, R–S–R′; more nucleophilic and easily oxidised.

Sulfoxide

R–S(=O)–R′ produced by mild oxidation (1 equiv H₂O₂) of a sulfide.

Sulfone

R–S(=O)₂–R′ formed by stronger oxidation (2 equiv H₂O₂) of a sulfide or sulfoxide.

Dimethyl sulfoxide (DMSO)

Polar aprotic solvent (CH₃)₂S=O; product of oxidising dimethyl sulfide.

Silyl ether

R–O–SiR′₃ derivative used to protect alcohols from bases/oxidants; removed by fluoride or acid.

TIPS ether

Triisopropylsilyl-protected alcohol (R-O-Si(i-Pr)₃); introduced with TIPS-Cl and Et₂N, removed by TBAF.

Protecting group

Temporary modification that masks a functional group to prevent unwanted reaction during synthesis.

MCPBA

meta-Chloroperoxybenzoic acid; common peroxyacid for alkene epoxidation.

Halohydrin cyclization

Base-induced intramolecular SN2 of a halohydrin yielding an epoxide and halide ion.

Acid-catalyzed epoxide opening

Protonation followed by nucleophilic attack at the more-substituted carbon with inversion; SN1-like regioselectivity.

Base-catalyzed epoxide opening

Nucleophilic attack at the less-substituted carbon under SN2 control; occurs with alkoxides, OH⁻, etc.

Regioselectivity of epoxide opening

Acidic conditions → attack more-substituted carbon; basic conditions → less-substituted carbon.

Grignard/organolithium epoxide reaction

Strong carbanions open epoxides at the less-substituted carbon, extending the carbon chain by two atoms after protonation.

Autoxidation of ethers

Slow air oxidation to peroxides and hydroperoxides; explosive—avoid distilling anhydrous ether to dryness.

Squalene epoxidase

Enzyme that converts squalene to 2,3-epoxysqualene in steroid biosynthesis.

Epichlorohydrin

Chlorinated epoxide used with bisphenol A to make epoxy-resin prepolymers.

Epoxy resin

Thermosetting polymer formed by curing bis-epoxide prepolymer with amine hardeners.

Trimethylsulfonium ion (SAM)

In biochemistry, S-adenosylmethionine acts as a sulfonium methyl donor in methylation reactions.

Hydrogen-bond donor/acceptor in ethers

Ethers are H-bond acceptors only (no O–H); alcohols are donors and acceptors, leading to higher bps.

Diethyl ether as Grignard solvent

Co-ordinates to Mg²⁺ in RMgX, stabilising the reagent while remaining inert to strong bases.