CHM 121: Ethers and Cyclic Ethers

Flashcards covering the nomenclature, physical properties, synthesis methods, and reactions of ethers and cyclic ethers (epoxides) based on the General Chemistry II lecture notes.

Ethers

Compounds where both sides of the oxygen are bound to an alkyl or aryl group ($R-O-R'$).

Physical Properties of Ethers

They are much less polar than alcohols, not soluble in water, have lower MP and BT than alcohols, are chemically inert, and are very flammable.

Ether Bond Angle

Ethers have a nearly tetrahedral bond angle, specifically $112^\circ$ in dimethyl ether.

Ether Oxygen Hybridization

The oxygen atom in an ether is $sp^3$-hybridized.

Common Nomenclature for Ethers

A naming system that treats each carbon chain as a branch off the oxygen, listing each side with a $-yl$ ending followed by the word "ether".

IUPAC Nomenclature for Ethers

A system where the longest carbon chain is the base name and the shorter chain is named as an "alkoxy" ($-oxy$ ending) substituent.

Industrial Diethyl Ether Preparation

Prepared by the sulphuric acid–catalysed dehydration of ethanol.

Williamson Ether Synthesis

The reaction of metal alkoxides and primary alkyl halides or tosylates; it is considered the best method for the preparation of ethers.

Sodium Hydride ($NaH$)

A strong base used to prepare metal alkoxides from alcohols for use in the Williamson Ether Synthesis.

Silver Oxide-Catalysed Synthesis

A one-step reaction of alcohols with direct alkyl halides in the presence of $Ag_2O$ to form an ether.

Pentaether Yield from Glucose

Glucose reacts with excess iodomethane in the presence of $Ag_2O$ to generate a pentaether in $85\%$ yield.

Acidic Cleavage

The process where strong acids like $HI$ or $HBr$ cleave ethers at elevated temperatures to produce an alkyl halide.

Acidic Cleavage Mechanism

Less hindered components undergo cleavage by $S_N2$, while tertiary ethers undergo cleavage by $S_N1$.

Epoxides (Oxiranes)

Three-membered cyclic ethers where the root "ir" comes from "tri" (3-membered), "ox" for oxygen, and "ane" for saturated.

Industrial Preparation of Ethylene Oxide

Prepared by the reaction of ethylene with oxygen at $300\,^\circ\text{C}$ using a silver oxide catalyst.

Peroxyacid Epoxide Synthesis

The preparation of an epoxide by treating an alkene with a peroxyacid, such as meta-Chloroperoxybenzoic acid.

Halohydrin Epoxide Synthesis

Treatment of a halohydrin (formed from $HO-X$ addition to an alkene) with base to give an epoxide via an intramolecular Williamson ether synthesis.

Acidic Ring-Opening

The addition of water to epoxides with dilute acid at room temperature to produce a 1,2-diol (vicinal diol).

Ring-Opening Stereochemistry

The mechanism involves the acid protonating oxygen and water adding to the opposite side, resulting in a trans-addition product.

Grignard Addition to Ethylene Oxide

A reaction that adds a $-CH_2CH_2OH$ group to the Grignard reagent’s hydrocarbon chain.

Crown Ethers

Large rings consisting of repeating ($-OCH_2CH_2-$) units with an electronegative central cavity that attracts cations.

Crown Ether Nomenclature ($x\text{-crown-}y$)

A system where $x$ is the total number of atoms in the ring and $y$ is the number of oxygen atoms.