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IUPAC Nomenclature of Saturated Hydrocarbon, Lowest Locant Rule, Straight Chain Hydrocarbon, Practice Problems & FAQs

IUPAC Nomenclature of Saturated Hydrocarbon, Lowest Locant Rule, Straight Chain Hydrocarbon, Practice Problems & FAQs

Hydrocarbons have been playing an important role in our daily lives for a very long time. A significant portion of these compounds are saturated hydrocarbons.

Can you guess some saturated hydrocarbons which we can find around us? Let me give you a hint! 

LPG or cooking gas majorly contains propane and butane which are saturated hydrocarbons.

Saturated hydrocarbons are the organic compounds that contain carbon-carbon single covalent bonds. In these compounds, there is the maximum number of hydrogen atoms present for every carbon atom. 

General formula of saturated hydrocarbon is

A general question comes to our mind about why it is necessary to give naming to organic compounds?

The IUPAC system of nomenclature was formed to create a universal standard for naming substances in order to improve communication.

TABLE OF CONTENT

  • Rules to assign IUPAC naming to saturated hydrocarbons
  • Longest Chain Rule
  • Lowest Set of Locants
  • Occurrence of the same substituent more than once
  • Naming of Different Substituents
  • Naming of Different Substituents At Equivalent Positions
  • Naming of The Complex Substituents
  • Recommended Video
  • Practice Problems
  • Frequently asked questions (FAQs)

Rules to assign IUPAC naming 

There are several rules to be followed to give naming to saturated hydrocarbons.

Rule 1 : Longest Chain Rule 

Select the longest continuous carbon chain in the molecule. This chain is known as the parent,

main, or principal chain. It can be a straight or branched chain.

Examples : 

Chain Explanation

Here, the longest zigzag chain consists

of eight carbon atoms. Hence, this is the

parent chain.

Here, the zigzag chain consists of six

carbon atoms and there are two side

Chains attached to it. Hence, this is the

parent chain.

Rule 2 : Lowest Set of Locants 

The numbering of the carbon atoms starts from the end which gives the lowest number to the carbon atom carrying the substituent.

Examples : 

Possibility 1 Possibility 2
The side chain is present on the fourth position. The side chain is present on the third position.
4-Ethylhexane (Incorrect) 3-Ethylhexane (Correct)

Rule 3 : Occurrence of the same substituent more than once 

Prefixes such as di, tri, etc are given to the substituents which are present twice, thrice respectively on the parent chain. The prefixes di, tri, and tetra are not considered in an alphabetical order.

Example :

Chain Explanation

Same substituent are present on 2nd and 4th position, So IUPAC name is

2,4-Dimethylhexane

Rule 4 : Naming of Different Substituents 

If more than one substituent is present then the substituents are arranged in their alphabetical order.

Examples :

Chain IUPAC name

4-Ethyl-2-methylheptane

3,3,6-Triethyl-7-methyldecane

Rule 5 : Naming of Different Substituents At Equivalent Positions

If two different substituents are present on the same position from the two ends then the substituents are named in such a way that the substituent which comes first in the alphabetical order gets the lowest number.

Examples :

Possibility 1 Possibility 2

In this compound, the parent chain has 7

carbons and two side chains in it at 3rd and

5th position. Here, the 3rd position has an ethyl side chain and 5th has a methyl side chain.

In this compound, the parent chain has 7

carbons and two side chains in it at 3rd and

5th position. Here, the 3rd position has a methyl side chain and the 5th has an ethyl side chain.

3-Ethyl-5-methylheptane (Correct) 5-Ethyl-3-methylheptane (Incorrect)

Rule 6 : Naming of The Complex Substituents 

Naming of the complex substituent is done when the substituent on the parent chain has a branched structure (i.e complex structure). These substituents are named as a substituted alkyl group and the carbon atom of this substituent attached to the parent chain is numbered as 1. Name of this type of substituent is written in brackets. Prefixes di, tri, tetra, etc are not considered in deciding the alphabetical order for simple substituents, but are considered for complex substituents. If more than one similar complex substituents are present, then the numeral prefixes bis, tris, tetrakis, etc., are used.

Examples :

Chain IUPAC name

5-(1,1,2-Trimethylpropyl)nonane

2,2,7-Trimethyl-4-(1-methylpropyl)nonane

4,6-Bis(1,1-dimethylethyl)nonane

Recommended Video : Saturated Hydrocarbons

Practice Problems

Q1. Write the IUPAC name of the given compound:

Solution :

Step 1: Choose the longest carbon chain and start numbering

The longest chain has 11 carbons. Now, the numbering should be done in such a way that the branched chain gets the least possible number. Thus, numbering should be done from left to right.

Step 2: Determine the position of the substituent

At the third position, there is a methyl group, and at the sixth position, there is a complex substituent i.e., 2,3-dimethylbutyl.

Now, since the branched chain has to be arranged in the alphabetical order of their name, the IUPAC name is 6-(2,3-dimethylbutyl)-3-methylundecane.

Q2. Write the IUPAC name of the compound  

Solution :

Step 1: Choose the longest carbon chain and start numbering

The longest chain has five carbon atoms.

Step 2: Determine the position of the substituent

At the third position, two t-butyl groups are attached, and at the second and fourth positions, two methyl groups each are attached. So, if we start numbering, the IUPAC name of the compound would be 3,3-bis(1,1-dimethylethyl)-2,2,4,4-tetramethylpentane.

Frequently asked questions

Q1. What is the difference between saturated and unsaturated hydrocarbons?

Answer : When organic compounds only contain carbon and hydrogen and all the carbon-carbon bonds are single covalent bonds are classified as Saturated hydrocarbons. Examples : Methane, Ethane etc.

When organic compounds consist of only carbon and hydrogen and contain at least one carbon-carbon, multiple bonds are classified as Unsaturated hydrocarbons. Examples : Ethene, Propyne etc.

Q2. What are the real life examples of saturated hydrocarbons ?

Answer : Saturated hydrocarbons are used in most of the fuels which are used to produce energy. These are also used in plastics, fibers. 

Q3. What is the primary source of saturated hydrocarbons ?

Answer : Fuels such as Petrol, Diesel, and LPG are obtained from fractional distillation of crude oil and all these fuels contain majorly saturated hydrocarbons.

Q4. is it possible to convert unsaturated hydrocarbons to saturated hydrocarbons ?

Answer : Yes, by Hydrogenation (reduction) of unsaturated hydrocarbons, multiple bonds of unsaturated hydrocarbons reduce to single covalent bonds to form saturated hydrocarbons.

Q5. What is the physical state of saturated hydrocarbons ?

Answer : At room temperature, Saturated hydrocarbons upto 4 carbons are gaseous in nature and from 5 to 17 carbon containing hydrocarbons are present in liquid state and even more carbon containing are solid in nature.

Related Topics

Nomenclature of functional groups Classification of organic compounds
Nomenclature of polyfunctional groups IUPAC nomenclature of unsaturated hydrocarbons

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