Nomenclature:
Nomenclature in chemistry is a set of rules that provides us with a systematic method to name various compounds. A worldwide accepted set of rules for nomenclature is given by the International Union of Pure and Applied Chemistry. Nomenclature is easy if you get the gist of how to choose a parent chain from a long carbon chain.
Nomenclature of ether strives on an easy concept of this choice. Let’s find out from the basics.
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What are Ethers?
Ether is defined as a class or group of organic compounds that follow the basic structure of oxygen surrounded by an aryl or alkyl groups on both its sides.
Did you know? Earlier ether was used as an anesthetic agent to make people unconscious during a medical procedure.
What is the Formula of Ether?
The general formula of ether:
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Where R and R’ are alkyl or aryl.
(Here, R1= R2 or R1=R2)
Which, in turn, drives us to the classification of ethers.
Did You Know?
Ether helped physicians to get a better idea of human physiology for refining surgical techniques.
Ether is used as a disinfectant before piercing the skin.
How are Ethers Classified?
Before getting into the classification, let’s first check your knowledge about what symmetry is?
In easy words, symmetry is an object when cut vertically from the center show identical two opposite faces.
Based on this concept and the number of carbon atoms in alkyl or aryl groups on both sides of the oxygen atom, ethers are classified as:
Symmetrical Ether:
If R1= R2, then it is known as symmetrical ether. Here, the substituent groups on both sides of the oxygen atom are the same by the formula.
For example:
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As the number of carbons and on the whole substituent groups on both sides of oxygen is the same, it follows symmetry.
Asymmetrical Ether:
If R1≠ R2, then it’s known as the asymmetrical. Here, the substituent groups on both sides of the oxygen atom are different by the formula.
For example:
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As the number of carbons that are the substituent groups on both sides of the oxygen atom is not the same by formula, it doesn’t follow symmetry.
What are the Types of Nomenclature of Ethers?
In easy language, we all speak a local dialect and the other which connects us to the world. The same is the case with nomenclature.
Nomenclature is a way or method of designating names for various compounds.
Here, we’re going to learn the various methods of naming the organic compounds which are as follows:
Trivial/Common Name Nomenclature of Ethers:
In this, we consider the following:
Alphabetical order of alkyl or aryl groups.
The complexity of the formula.
Ends with the prefix 'ether.'
For example:
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Points to Remember:
Here, the substituent groups are methyl and phenyl.
M is alphabetically before P.
There isn’t any branching.
Hence, the common name of ether = Methyl phenyl ether.
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Points to Remember:
Here, substituent groups are isopropyl and ethyl.
E is alphabetically before i.
There is secondary branching in the compound in the alpha carbon.
Hence, the common name of ethers= Ethyl isopropyl ether.
Cyclic Ethers Follow This Below:
Cyclic ether with 2 carbons = Epoxide.
Cyclic ether with 4 carbons with 2 double bonds = Furan.
Cyclic ether with 5 carbons with 2 double bonds = Pyran.
Cyclic ether with 4 carbons with 2 oxygen atoms = Dioxane.
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IUPAC Naming of Ethers:
What are the steps proposed by IUPAC in naming ethers?
The naming of ethers is done in the following steps, the rules underlying the nomenclature of ethers are:
Select the substituent group with the maximum number of carbon atoms.
The substituent group with lesser carbon atoms is written as first words with the addition of ‘oxy’.
When multiple substituent groups are the same, then suffixes like di, tri, etc. are used.
For example:
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Points to Remember:
Here, substituent groups are methyl and ethyl.
Methyl being the one with lesser carbon atoms than the ethyl group, will have the prefix ‘oxy’ attached to it.
There isn’t any branching.
Hence, the IUPAC name of ether = Methoxyethane
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Points to Remember:
Here, substituent groups are methyl and ethyl.
Methyl being the one with lesser carbon atoms than the ethyl group will have the prefix ‘oxy’ attached to it.
There isn’t any branching.
There are two methyl groups adjacent to oxygen atoms.
IUPAC name of ether = Dimethoxyethane.
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FAQs on Ether Nomenclature
1. What are ethers and what is their general chemical formula?
Ethers are a class of organic compounds where an oxygen atom is connected to two alkyl or aryl groups. These groups can be identical or different. The general formula for an ether is R–O–R', where R and R' represent the alkyl or aryl groups.
2. What are the two main systems for the nomenclature of ethers?
The two primary systems used for naming ethers are:
- Common or Trivial Nomenclature: An older, simpler system where the alkyl/aryl groups are named alphabetically followed by the word 'ether'.
- IUPAC (International Union of Pure and Applied Chemistry) Nomenclature: A systematic method that treats the ether as a hydrocarbon derivative with an alkoxy substituent.
3. How are ethers named using the common nomenclature system?
In the common system, you identify the two alkyl or aryl groups attached to the oxygen atom. These group names are written in alphabetical order, followed by the word 'ether'. For instance, in CH₃–O–CH₂CH₃, the groups are 'ethyl' and 'methyl'. Alphabetically, it becomes Ethyl methyl ether. If both groups are the same, like in CH₃CH₂-O-CH₂CH₃, the prefix 'di-' is used, as in Diethyl ether.
4. What are the official IUPAC rules for the nomenclature of ethers?
The IUPAC system follows the 'alkoxyalkane' format. The rules are:
- Identify the longest carbon chain attached to the oxygen atom. This chain is considered the parent alkane.
- The smaller alkyl group, along with the oxygen atom, is treated as a substituent called an alkoxy group (e.g., CH₃O– is 'methoxy', C₂H₅O– is 'ethoxy').
- Name the alkoxy group as a prefix to the parent alkane, indicating its position with a number if necessary. For example, CH₃–O–CH₂CH₃ is named Methoxyethane.
5. How are symmetrical and asymmetrical ethers different, and how does this affect their naming?
The difference lies in the groups attached to the oxygen atom:
- Symmetrical ethers have two identical alkyl or aryl groups (R = R'). Their naming is straightforward in both systems, e.g., Diethyl ether (common) or Ethoxyethane (IUPAC).
- Asymmetrical ethers have two different groups (R ≠ R'). Naming them requires a choice. In the common system, the groups are listed alphabetically (e.g., Ethyl methyl ether). In the IUPAC system, the larger group dictates the parent alkane name, while the smaller group becomes the alkoxy prefix (e.g., Methoxyethane).
6. What is the role of the 'oxy' suffix in the IUPAC nomenclature of ethers?
In the IUPAC system, the suffix '-oxy' is added to the root name of the smaller alkyl group to transform it into a substituent name. For example, a methyl group (CH₃–) becomes a methoxy group (CH₃O–), and an ethyl group (C₂H₅–) becomes an ethoxy group (C₂H₅O–). This 'alkoxy' group is then used as a prefix to name the parent alkane.
7. Can you provide some examples of ether nomenclature using both common and IUPAC names?
Certainly. Here are a few examples that show the comparison:
- CH₃–O–CH₃: Common name is Dimethyl ether; IUPAC name is Methoxymethane.
- CH₃CH₂–O–CH₂CH₃: Common name is Diethyl ether; IUPAC name is Ethoxyethane.
- CH₃–O–CH₂CH₂CH₃: Common name is Methyl propyl ether; IUPAC name is 1-Methoxypropane.
- C₆H₅–O–CH₃: Common name is Methyl phenyl ether (or Anisole); IUPAC name is Methoxybenzene.
8. Why is the smaller alkyl group chosen as the alkoxy substituent in IUPAC nomenclature, and not the larger one?
The fundamental principle of IUPAC nomenclature is to identify the longest continuous carbon chain as the parent hydrocarbon. This chain forms the base name of the compound. Consequently, the ether's larger alkyl group is usually designated as this parent chain. The remaining, smaller alkyl group, along with the oxygen atom, is then treated as a substituent (the alkoxy group) attached to this main chain. This maintains consistency with the general rules for naming organic compounds.
9. How is the nomenclature of cyclic ethers different from that of open-chain ethers?
Unlike open-chain ethers named as 'alkoxyalkanes', cyclic ethers are named as heterocycles. The oxygen atom is considered part of the ring itself. In the IUPAC system, the prefix 'oxa-' is used to denote the oxygen atom replacing a carbon in the ring. For example, a six-membered ring with one oxygen is named Oxane. Many simple cyclic ethers also have widely accepted common names, such as Oxirane (for a three-membered ring, also called an epoxide) and Furan (a five-membered aromatic ring with oxygen).
10. In a complex molecule with multiple functional groups, how is the ether group prioritised during IUPAC naming?
The ether linkage (–OR) has a relatively low priority in the IUPAC system. It ranks below functional groups like carboxylic acids, esters, aldehydes, ketones, and alcohols. When a higher-priority functional group is present in the molecule, that group determines the parent name and suffix. The ether group is then always treated as a substituent, named with an alkoxy prefix, and its position is indicated by a number. For example, 4-methoxybutan-2-ol has an alcohol (–ol) as the principal group and methoxy as a substituent.
