Nomenclature of Alcohols, Phenols and Ethers: Rules and Examples, FAQs

Alcohols Ethers and Phenols are the categories of organic compounds. These compounds are used extensively in a variety of household businesses. Alcohol is created when the hydroxyl (-OH) group forms a bond with the saturated carbon atom. Ether is created when alcohol is dehydrated. These are the classes of organic compounds that are used in a variety of residential and industrial environments.

Nomenclature – Alcohols, Phenols, and Ethers

The organic compounds with the “hydroxyl (-OH)” as a functional group are termed Alcohols. The “carbonyl” carbon atom is the carbon atom that is directly bound to the -OH group. However, the carbonyl carbon (carbon bonded to OH) is what distinguishes “primary,” “secondary,” and “tertiary” alcohols.

What are Alcohols ?

Alcohol is referenced by the name of its parent alkane. -a nol and a number designating the position of the -OH group on the chain are used in place of the -ane suffix of the parent hydrocarbon chain. Whereas this saturated carbon atom is joined to a hydroxyl (-OH) group, alcohol is created.

Alkanols, which have the general formula R-OH, is the generic name for alcohol according to the IUPAC (International Union of Pure and Applied Chemistry) Nomenclature.

Alcohols occur frequently in nature, with ethyl alcohol (ethanol), the primary component of alcoholic beverages, being the most well-known. In the homologous sequence of alcohols, methanol (CH₃OH) and ethanol (CH₃CH₂OH) are the first two compounds.

Classification of Alcohols

Alcohol can be divided into three categories based on how many hydroxyl groups are linked, 

• Monohybrid Alcohol: The standard formula for monohydric alcohols is C_nH_2n+1OH, where n is 1, 2, etc. They can alternatively be expressed as R-OH, where R stands for an alkyl group. They have a single -OH group.  An example is CH₃CH₂-OH.
• Dihybrid Alcohol: The standard formula for dihydric alcohols is (CH₂)_n(OH)₂, where n is 2, 3, 4, etc. We call them “glycols” because of their sweet flavor. We can categorize them as α, β, ϒ…..ω-glycols, etc. depending on the relative positions of the two hydroxyl groups. They have two -OH groups. An example is 1,2-Ethanediol.
• Trihybrid Alcohol: Trihydric alcohols have the standard formula (CH₂)_n(OH)₃, where n is 3, 4, 5, etc. There is no overall nomenclature guideline in this system. The IUPAC has only one rule. These trihydric alcohols are known as Alkanethiols in the IUPAC classification system. We denote the position of the -OH group by Arabic numerals.

Alcohols are divided into three categories based on the number of carbon atoms that are bound to the carbon that is in direct contact with the -OH group. 

• In Primary Alcohol, one carbon atom is linked directly. 
• In Secondary Alcohol, two carbon atom is linked directly. 
• In Tertiary Alcohol, three carbon atom is linked directly.  

IUPAC Nomenclature for Alcohols

Common names for alcohols with one to four carbon atoms typically include the word alcohol after the name of the alkyl group. 

The International Union of Pure and Applied Chemistry (IUPAC) states that. -anol replaces the parent hydrocarbon chain’s -ane suffix. Basic IUPAC guidelines for identifying alcohol include:

• The parent compound is decided based on the length of the longest continuous chain (LCC) of carbon atoms bearing the -OH group.

• The chain is numbered from the end closest to the -OH group, with the -OH group occupying the lowest position in the chain (lowest locant rule).

• The parent hydrocarbon’s alkane chain’s -ane suffix is changed to -anol, and the name of the parent hydrocarbon is appended with the number denoting the position of the OH group.

• 4. The carbon atom that is linked to the -OH group is referred to as C1 in cyclic alcohols, but the number 1 is not present in the nomenclature. Substituents are given names and numbers, as with alkanes.

• Suffixes like “diol” and “triol” are used when there are many -OH groups present in a single molecule (polyhydroxy alcohols). When naming polyhydroxy alcohols, the parent alkane’s final ‘-e’ is maintained.

• The absolute configuration appears at the start of the name if the OH group is linked to a chiral centre. Additionally, the E and Z configuration should be addressed when necessary, if there is a double bond.

• The ring is numbered clockwise or anticlockwise depending on which orientation provides the following substituent for the lower number when other groups are present.

Common System: Alkyl alcohol is the common name for monohydric alcohols. After the name of the alkyl group is present in the molecule, we can add the name alcohol to get their names. For instance, the CH3-OH molecule combines an alcohol group and one methyl group. As a result, we refer to it as methyl alcohol.

In the standard method, we simply append the word “Glycol” to the end of the name of the alkene to name the – glycols. The names of the – glycols, in contrast, are the same as those of the equivalent polyethylene glycols.

Phenols

Phenols are organic compounds that have an aromatic ring of carbon atoms linked to a hydroxyl (-OH) group. Ar-OH is the designation for phenols. It can be divided into mono-, di-, tri-, or polyhydric phenols depending on how many hydroxyl groups are joined to the aryl group. 

When the -OH group replaces the hydrogen atom in a benzene molecule, phenol is created.

Classification of Phenols

Phenols are divided into three groups according to the number of attached hydroxyl groups, 

• Monohydric phenols – The phenols having a single -OH group in the compound are termed Monohydric phenols.
• Dihydric phenols – The phenols having two -OH groups, either the “ortho-,” “meta-” or “para-” derivatives in the compound, are termed as Dihydric phenols. 
• Trihydric phenols – The phenols having three -OH groups in the compound are termed Trihydric phenols.

IUPAC Nomenclature of Phenols

Similar to how the names for aliphatic alcohols are generated, the IUPAC term for phenol is hydroxybenzene. It is usually referred to as carbolic acid.

• The presence and number of the hydroxyl group linked to the benzene ring are specified.
• If more than one hydroxyl group is present, then numerical prefixes such as di, tri, and tetra denote the number of similar hydroxyl groups attached to the benzene ring.

• The various functional groups in substituted phenols are numbered according to the position at which the hydroxyl group is added.
• The nomenclature of phenols also uses terms like -ortho, which means that a functional group is attached to the adjacent carbon atom to which a -OH group is attached. -meta, which means that a functional group is attached to the second carbon atom from the hydroxyl group, and -para, which means that a functional group is attached to the third carbon atom from the hydroxyl group.

Common system: The prefix ortho (o-), meta (m-), and para (p-) are used in the common system to denote the position of the substituent relative to the -OH group on the benzene ring.

Ethers 

Ethers are organic molecules in which two hydrocarbon groups are linked to both ends of the oxygen atom (alkyl or aryl). The general formula for ether is R-O-R′. The hydrocarbon group may be the same as R or different, represented by the R′ in the formula. 

Classification of Ethers

Ether can be divided into two categories based on the aryl or alkyl group type connected to the oxygen atom.

• Symmetrical Ether: The aryl or alkyl group that is connected to either side of the oxygen atoms is identical to that of the simple ether, which is another name for it. Examples include C₂H₅OC₂H₂, CH₃OCH₃, and others.
• Unsymmetrical Ether: This is also known as mixed either because there are different aryl or alkyl groups connected to either side of the oxygen atoms. A few examples include C₂H₅OC₆H₅, CH₃OC₂H₅, and others.

IUPAC Nomenclature of Ethers

• One of the alkoxy (alkyl with oxygen) groups is handled as a substituent attached to a parent chain, with the longest carbon chain selected as the parent chain.
• The oxygen atom is a component of the alkyl group, which has fewer carbon atoms than it does, and combined, these two groups make up the alkoxy group.
• Alkyl substituents in the IUPAC system have a -oxy ending in place of the -yl. For instance, -OCH₃ methoxy is -CH₃ methyl, while -OCH₂CH₃ ethoxy is -CH₂CH₃ ethyl.

• Alkoxy (-O-R) groups are not prioritized in the list of functional groups because they are thought of as substituents. Therefore, they leave the parent chain’s suffix. 
  The parent chain is changed from “ane” to “ol,” and the -OH group is given priority. The -OR group, on the other hand, is appended as a prefix in alphabetical order and has no priority.

• The ether’s substituents are identified alphabetically by name.

Common System: The two aryl or alkyl groups connected to the oxygen atoms can be named separately in alphabetical sequence, and then we can add the suffix “ether” to create the common names of ethers. We employ the “di” prefix before the alkyl or aryl group name in the case of symmetrical ethers.

The prefix -di is used for symmetrical ethers. If the names of the alkyl groups are different, spaces should be left between them and before the term ether.

Solved Examples on Alcohols, Phenols, and Ethers

Example 1: What is the IUPAC name of the given compound?

Solution: 

The prefix tri- is chosen because there are three -NO₂ groups. Considering all things, the provided compound’s IUPAC name is 2,4,6-trinitrophenol.

Example 2: What is the IUPAC name of the given compound?

Solution:

The parent chain includes five carbon atoms, and at positions 1, 2, and 4 there are -OH, ethyl, and methyl groups. Therefore, the provided compound’s IUPAC name is 2-Ethyl-4-methyl-1-pentanol.

Example 3: What is the IUPAC name of the given compound?

Solution:

The shorter alkyl group on the oxygen atom’s end forms the alkoxy substituent. The alkoxy group gets the lowest locant in the parent chain because of how the locants are numbered. The IUPAC name is written with numbers and words separated by hyphens, and the substitutes are listed alphabetically (-). The specified compound’s IUPAC name is 1-bromo-5-ethoxyl-3-methylhexane.

FAQs on Alcohols

Question 1: What is the priority order of various functional groups in IUPAC nomenclature?

Answer: 

According to the IUPAC system of naming, the functional groups are prioritized in the following order, 

Carboxylic Acid > Sulfonic Acid > Esters > Acid Halides > Amides > Cyanides > Aldehyde > Ketones > Alcohols > Amines > Alkynes > Alkenes > Alkanes.

Question 2: What is the General Formula of Alcohol?

Answer: 

Alcohols are organic compounds with an aliphatic carbon atom and the functional group “hydroxyl (-OH)” attached. Since all alcohols contain the functional group -OH, they are all represented by the generic formula R-OH, where R is an alkyl group.

Question 3: What is a Functional Group?

Answer: 

The group of atoms in a molecule known as a functional group controls the chemical behavior of the molecule. It establishes the molecule’s chemical characteristics.

Question 4: Why is Phenol more acidic than Ethanol?

Answer: 

Because phenol forms phenoxide ions while losing H+ ions, while ethanol forms ethoxide ions, hence phenol is more acidic than ethanol. Phenol is more acidic than ethanol because resonance stabilizes the phenoxide ion.

Question 5: What is the IUPAC nomenclature of m-cresol?

Answer: 

3-Methylphenol is the name given to m-cresol by IUPAC. In relation to the -OH group, the methyl group is located at the second carbon atom.