There are reasons how each one of us got our names. Isn’t it? Similarly, there are reasons behind how alcohol, phenol and ethers got their name. Are you familiar with the nomenclature of these organic compounds? Well, let’s find out! In this chapter, we will look at the nomenclature of alcohol, phenols and ethers. We will cover the IUPAC rules and see a few examples for the same. Let us start with the nomenclature of alcohols.
Nomenclature of Alcohols
We know alcohols are of three major classes. They are:
- Monohydric Alcohol
- Dihydric Alcohol
- Trihydric Alcohol
We will now discuss the nomenclature of these alcohols.
1) Monohydric Alcohol
Monohydric alcohols have the general formula CnH2n+1OH where n = 1, 2, etc. We can also represent them as R-OH where R describes an alkyl group. There are three systems for the nomenclature of Monohydric Alcohol.
- Common System: In this system, we name the monohydric alcohols as Alkyl Alcohol. We get their names by adding the name alcohol after the name of the alkyl group present in the molecule. Example: The compound CH3-OH has one methyl group with an alcohol group. Hence, we call it Methyl Alcohol.
- Carbinol System: In this system, methyl alcohol (CH3OH) gets the name Carbinol while other alcohols get their names as alkyl or aryl derivatives of carbinol. Example: CH3-CH2-OH is methylcarbinol and CH3-CH2-CH2-OH is Ethylcarbinol.
- IUPAC System: In IUPAC nomenclature, we term the alcohols as Alkanols. We get the name of any alcohol by replacing the last ‘e’ from the name of the corresponding alkane by the suffix ‘–ol’. Then, we select the longest carbon chain containing the OH group as the parent chain. We, then, number the longest chain in such a way that the carbon atom carrying the OH group gets the smaller number. After. this, we show the position of the substituents by suitable numbers allotted to their respective carbon atom.
Example: The compound CH3-OH is Methyl Alcohol but in the IUPAC, we call it as Methanol. Here, we replace the last ‘e’ of the methane by ‘ol’ which indicates the presence of an alcohol group. In the naming of the Cyclic monohydric alcohols prefix, ‘cyclo’ is used in writing the common or the IUPAC names of the straight chain alcohols.
2) Dihydric Alcohol
Dihydric alcohols have the general formula of (CH2)n(OH)2, where n= 2,3,4…. etc. Because of their sweet taste, we refer to them as Glycols. Depending upon the relative position of the two hydroxyl group, we can classify them as α, β, ϒ…..ω-glycols, etc. Let us look at the system of their nomenclature.
- Common System: In common system, we name the α- glycols by adding the word Glycol after the name of the alkene. In contrast β, ϒ … ω – glycols get their names as the corresponding polymethylene glycols. Example:
|Trimethylene glycol ( A β-glycol)||pentamethylene glycol|
- IUPAC system: In this system, we name the glycols as Diols and their class name is Alkanediols. We use Arabic numerals to indicate the two hydroxyl group positions.
3) Trihydric Alcohol
The general formula of trihydric alcohols is (CH2)n(OH)3 where n = 3, 4, 5 …etc. In this system, we do not have any general rule of nomenclature. So, there is only one IUPAC rule. In this IUPAC system of trihydric alcohol, we call them as Alakanetriols. We use Arabic numerals to indicate the position of the OH group.
Nomenclature of Phenols
The simplest derivative of benzene is Phenol. It is the common name as well as an accepted IUPAC name. Both in the common and in the IUPAC system, we name the substituted phenols as the derivatives of phenols.
In the common system, we indicate the substituent position present on the benzene ring with respect to –OH group by adding the prefix such as ortho (o-) for 1:2, meta (m-) for 1,3 and para (p-) for 1,4.
However, in the IUPAC system, we use Arabic numerals to indicate the position of the substituent w.r.t –OH group. The carbon carrying the OH group gets the number 1. The phenols having a carbonyl group such as aldehyde, ketonic, carboxyl or an ester group get their names as hydroxyl derivatives of the parent aromatic compound.
Nomenclature of Ethers
- Common System: We get the common names of ethers by naming the two alkyl or aryl groups linked to the oxygen atom as separate words in alphabetical order and adding the word ether. In case of symmetrical ethers, we use the prefix di before the name of the alkyl or the aryl group.
- IUPAC system: In the IUPAC system, ethers are Alkoxyalkanes. The ethereal oxygen is taken with the smaller alkyl group and forms a part of the alkoxy group. On the other hand, the larger alkyl group is taken to be the part of the alkane.
Solved Example for You
Q: How do we name dihydric and trihydric phenols according to the IUPAC system?
Ans: In the IUPAC system, di-, Tri- and polyhydric phenols get the names of Hydroxyl Derivatives of Benzene.