Ether: Difference between revisions

In [[organic chemistry]], '''ethers''' are a class of [[organic compound|compound]]s that contain an ether [[functional group|group]], a single [[oxygen]] atom bonded to two separate carbon atoms, each part of an [[organyl]] group (e.g., [[alkyl]] or [[aryl]]). They have the general formula {{chem2|R\sO\sR′}}, where R and R′ represent the organyl groups. Ethers can again be classified into two varieties: if the organyl groups are the same on both sides of the oxygen atom, then it is a simple or symmetrical ether, whereas if they are different, the ethers are called mixed or unsymmetrical ethers.<ref>{{GoldBookRef|title=ethers|file=E02221}}</ref> A typical example of the first group is the [[solvent]] and [[anaesthetic]] [[diethyl ether]], commonly referred to simply as "ether" ({{chem2|CH3\sCH2\sO\sCH2\sCH3}}). Ethers are common in organic chemistry and even more prevalent in [[biochemistry]], as they are common linkages in [[carbohydrate]]s and [[lignin]].<ref>{{cite book|title=The Ether Linkage|year=1967|editor=Saul Patai|isbn= 978-0-470-77107-5|doi=10.1002/9780470771075|publisher=John Wiley & Sons|series=PATAI'S Chemistry of Functional Groups}}</ref>

==Structure and bonding==

Ethers feature bent {{chem2|C\sO\sC}} linkages. In [[dimethyl ether]], the [[Molecular geometry#Bonding|bond angle]] is 111° and C–O distances are 141&nbsp;[[Picometre|pm]].<ref>{{cite journal |doi=10.1039/b405684a|title=Dichlorosilane–Dimethyl Ether Aggregation: A New Motif in Halosilane Adduct Formation|year=2004|last1= Vojinović|first1=Krunoslav|last2=Losehand|first2=Udo|last3=Mitzel|first3=Norbert W.|journal=Dalton Trans.|issue=16|pages=2578–2581|pmid=15303175}}</ref> The barrier to rotation about the C–O bonds is low. The bonding of oxygen in ethers, alcohols, and water is similar. In the language of [[valence bond theory]], the hybridization at oxygen is sp³.

Ethers can be symmetrical of the type ROR or unsymmetrical of the type ROR'. Examples of the former are [[dimethyl ether]], [[diethyl ether]], [[dipropyl ether]] etc. Illustrative unsymmetrical ethers are [[anisole]] (methoxybenzene) and [[dimethoxyethane]].

In the [[IUPAC Nomenclature]] system, ethers are named using the general formula ''"alkoxyalkane"'', for example CH₃–CH₂–O–CH₃ is [[methoxyethane]]. If the ether is part of a more-complex molecule, it is described as an alkoxy substituent, so –OCH₃ would be considered a ''"[[methoxy]]-"'' group. The simpler [[alkyl]] radical is written in front, so CH₃–O–CH₂CH₃ would be given as ''methoxy''(CH₃O)''ethane''(CH₂CH₃).

IUPAC rules are often not followed for simple ethers. The trivial names for simple ethers (i.e., those with none or few other functional groups) are a composite of the two substituents followed by "ether". For example, ethyl methyl ether (CH₃OC₂H₅), diphenylether (C₆H₅OC₆H₅). As for other organic compounds, very common ethers acquired names before rules for nomenclature were formalized. Diethyl ether is simply called ether, but was once called ''sweet oil of vitriol''. Methyl phenyl ether is [[anisole]], because it was originally found in [[aniseed]]. The [[aromatic]] ethers include [[furan]]s. [[Acetal]]s (α-alkoxy ethers R–CH(–OR)–O–R) are another class of ethers with characteristic properties.

==Physical properties==

{| style="width:100%;" class="wikitable"

==Reactions== <!-- This section is linked from [[Organic reaction]] -->

The C-O bonds that comprise simple ethers are strong. They are unreactive toward all but the strongest bases. Although generally of low chemical [[reactivity (chemistry)|reactivity]], they are more reactive than [[alkanes]].

===Cleavage===

{{see also|Ether cleavage}}

:ROCH₃ + HBr → CH₃Br + ROH

These reactions proceed via [[onium compounds|onium]] intermediates, i.e. [RO(H)CH₃]⁺Br⁻.

=== Lewis bases ===

Ethers serve as [[Lewis base]]s. For instance, [[diethyl ether]] forms a [[Coordination complex|complex]] with [[boron trifluoride]], i.e. borane diethyl etherate ({{chem2|BF3*O(CH2CH3)2}}). Ethers also coordinate to the [[magnesium|Mg]] center in [[Grignard reagent]]s. [[Tetrahydrofuran]] is more basic than [[Open-chain compound|acyclic]] ethers. It forms with many [[transition metal ether complex|complex]]es.

===Dehydration of alcohols===

The [[dehydration reaction|dehydration]] of [[Alcohol (drug)|alcohol]]s affords ethers:<ref>{{cite book |title=Organic chemistry |last1=Clayden |last2=Greeves |last3=Warren |year=2001 |publisher=Oxford University Press |isbn=978-0-19-850346-0 |page=[https://archive.org/details/organicchemistry00clay_0/page/129 129] |url-access=registration |url=https://archive.org/details/organicchemistry00clay_0/page/129}}</ref>

: R–CH₂–CH₂(OH) → R–CH=CH₂ + H₂O

===Electrophilic addition of alcohols to alkenes===

==Important ethers==

|-

| [[Ethylene oxide]]

| A cyclic ether. Also the simplest [[epoxide]].

| A linear polyether, e.g. used in [[cosmetics]] and [[pharmaceuticals]].

|-

| [[Polypropylene glycol]]

| A linear polyether, e.g. used in [[polyurethanes]].