Properties of Ether

Introduction

Ethers are organic compound classes that contain an ether group, an oxygen atom connected to two aryl or alkyl groups. They do have the general formula as R - O - R′, where R and R′ represent the aryl or alkyl groups. Ethers can be classified further into two varieties. Suppose, if the alkyl groups are the same on both sides of an oxygen atom, then it is known as a simple or symmetrical ether. On the other side, if they are different, ethers are referred to as mixed or unsymmetrical ethers.


A typical example of the first group is solvent and anesthetic diethyl ether simply referred to as "ether" (CH3 - CH2 - O - CH2 - CH3). In organic chemistry, ethers are common and even more prevalent in biochemistry, as they are common linkages in lignin and carbohydrates. The structure of ethers is similar to the structure of alcohol, and both alcohols and ethers are similar in structure to water.


The general formula of ethers can be R-O-R, R-O-Ar, or Ar-O-Ar, where Ar represents an aryl group, and R represents an alkyl group.


Structure of Ether

The C-O-C linkage is characterized by the bond angles of 104.5 degrees, with the C-O distances being about 140 picometres. The ether's oxygen is more electronegative than that of carbons. Therefore, alpha hydrogens are more acidic than in the regular hydrocarbon chains.

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Nomenclature of Ethers

To name ether, there are two ways. One of the most common ways is to identify the alkyl groups on either side of the oxygen atom in alphabetical order, writing as "ether." For example, ethyl methyl is the one that has an ethyl group and a methyl group on any side of the oxygen atom. If two alkyl groups are identical, the ether is called di (alkyl) ether. And, for suppose, diethyl ether is the one with an ethyl group on each side of the oxygen atom.

The other way of naming is formal by the IUPAC method. Here, the form is short alkyl chain, oxy, and long alkyl chain. As an example, the IUPAC name of ethyl methyl ether would be methoxy ethane.

The stem of the compound is called oxacycloalkane in cyclic ethers. "Oxa" is an indicator of the carbon replacement by oxygen in the ring. Oxacyclopentane is an example of a five-membered ring, where there are four carbon and one oxygen atoms.

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Properties of Ether

Ethers are rather nonpolar because of the presence of an alkyl group on either side of the central oxygen. There exist the bulky alkyl groups adjacent to it means the oxygen atom is highly unable to participate in hydrogen bonding. Thus, ethers have lower boiling points when compared to alcohols having the same molecular weight. 

As the ethers alkyl chain becomes longer; however, the difference in boiling points becomes smaller. This happens due to the effect of increased Van der Waals interactions as the number of carbons increases. And thereby, the number of electrons increases as well. The two lone pairs of electrons in the oxygen atoms allows for ethers to form hydrogen bonds reacting with water. Ethers are much more polar than alkenes, whereas it is not as polar as alcohols, esters, or amides of comparable structures.

The physical and chemical properties of ether are given below.


Physical Properties of Ethers

Ethers physical properties can be described as below.

  • An ether molecule contains a net dipole moment. This can be attributed to the C - O bond polarity.

  • Ether's boiling point is comparable to the alkanes. However, it is very low compared to alcohols of comparable molecular mass. Besides, this is the fact of the polarity of the C-O bond.

  • Ether's miscibility with water resembles those of alcohol.

  • The water molecules of ether are miscible in water. Also, we can attribute this to the fact like alcohols, the ether's oxygen atom can also form hydrogen bonds with a water molecule.


Chemical Properties of Ethers

Generally, ethers undergo chemical reactions in two ways. Let us look at it in the below section.

Cleavage of C-O bond

Generally, ethers are very unreactive in nature. When we add an excess hydrogen halide to the ether, cleavage of the C-O bond takes place. It results in the formation of alkyl halides. The order of reactivity is as below.

HI > HBr > HCl

R-O-R + HX --> RX + R-OH


Electrophilic Substitution

The ether's alkoxy group activates the aromatic ring at para and ortho positions for electrophilic substitution. Some common electrophilic substitution reactions are Friedel Crafts reaction, halogenation, and a few more.


Halogenation Reaction of Ethers

Ethers of aromatic type undergo halogenation. For suppose, Bromination - when we add halogen atoms in the presence or absence of a catalyst.

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Friedel Crafts Reaction of Ethers

Aromatic ethers undergo Friedel Crafts reaction. For example, the addition of an acyl or alkyl group when we introduce it to an acyl or alkyl halide in the presence of a Lewis acid as a catalyst.

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FAQ (Frequently Asked Questions)

1. Mention Some Key Points of Ether?

Few of the ether's key points can be mentioned as,

  • Ethers have low boiling points relatively because of their inability to form hydrogen bonds with each other.

  • Because of the electronegativity difference between the oxygen and carbon atoms of ether, slightly, the molecule is polar.

  • While ethers have low reactivity overall, the two lone pairs of electrons on the oxygen atom give certain reactivity to the ether molecule; the ether molecule is subjected to react with strong acids and serves as a Lewis base.

2. What are Polyethers?

Polyethers are the compounds having more than one ether group and have been used as impression materials in dentistry.

The examples of small polyethers are crown ethers. Some toxins are produced by dinoflagellates like brevetoxin and ciguatoxin, which are extremely large and are referred to as a ladder or cyclic polyethers.

Generally, polyether refers to the polymers containing the ether functional group in their main chain. Usually, glycol is reserved for a low to medium range molar mass polymer when the nature of the end-group, which is usually a hydroxyl group, still matters. The terms like "oxide" or others are used for high molar mass polymers when end-groups no longer affect the properties of the polymer.