Question

How many constitutional isomers are there for ${\mathrm{C}}_6{\mathrm{H}}_{12}$?

Answer 1

Isomerism

• Isomers are compound that has the same molecular formula, that is they have the same number of atoms of each element but their arrangement is different.
• Isomers may or may not have the same physical and chemical properties.
• Constitutional isomers, also known as structural isomers, are compounds with the same molecular formula but with a different structure.

Constitutional isomers for ${\mathrm{C}}_6{\mathrm{H}}_{12}$

• Cyclic hydrocarbon is in which carbon atoms are arranged in the form of a ring.
• The general molecular formula of alkene and cycloalkane is ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}}$
• The given compound formula can either be of alkene or cycloalkane

1. Cyclohexane

Here, six carbon atoms are arranged in the form of a ring.

• In the three compounds given below, there is a double bond between two carbon atoms in the main chain and two methyl groups are also present in the main chain.

2. 2,3 - Dimethyl-1-butene

Here, the double bond between the first and second Carbon atoms in the main chain and two Methyl groups are also present in the second and third Carbon atoms.

3. 3,3 - Dimethyl-1-butene

Here, the double bond between the first and second Carbon atoms in the main chain and two Methyl groups are also present in the third Carbon atom.

4. 2,3 - Dimethyl-2-butene

Here, the double bond between the second and third Carbon atoms in the main chain and two Methyl groups are also present in the second and third Carbon atoms.

• In the three compounds, a ring of four carbon atoms and two methyl groups are present at different positions.

5. 1,1-Dimethylcyclobutane

Here, a ring of four carbon atoms and two methyl groups are present at one carbon atom

6. 1,2-Dimethylcyclobutane

Here, a ring of four carbon atoms and two methyl groups are present at the first and second carbon atoms.

7. 1,3-Dimethylcyclobutane

Here, a ring of four carbon atoms and two methyl groups are present at the first and third carbon atoms.

• In this compound, there are four carbon atoms in the main chain with a double bond at the first carbon atom and one ethyl group is present at the second carbon atom.

8. 2-Ethyl−1−butene:

• In this compound, a ring of four carbon atoms and one ethyl group is present as the first carbon atom of the ring.

9. Ethylcyclobutane

• In the following three compounds, there is the main chain of six carbon atoms and one double bond is present at a different position

10. 1-Hexene

Here, the main chain of six carbon atoms and one double bond is present between the first and second atoms.

11. 2-Hexene

Here, the main chain of six carbon atoms and one double bond is present between the second and third atoms.

12. 3-Hexene

Here, the main chain of six carbon atoms and one double bond is present between the third and fourth atoms.

• In the following six compounds, there is the main chain of five carbon atoms in which methyl groups and the position of the double bond change.

13. 2-Methyl-1-pentene

Here, the double bond between the first and second Carbon atom in the main chain the Methyl group is present in the second Carbon atom.

14. 2-Methyl-2-pentene

Here, the double bond between the second and third Carbon atoms in the main chain and the Methyl group is present in the second Carbon atom.

15. 3-Methyl-1-pentene

Here, the double bond between the first and second Carbon atom in the main chain and the Methyl group is present in the third Carbon atom.

16. 3-Methyl-2-pentene

Here, the double bond between the second and third Carbon atoms in the main chain and the Methyl group is present in the third Carbon atom.

17. 4-Methyl-1-pentene

Here, the double bond between the first and second Carbon atom in the main chain and the Methyl group is present in the fourth Carbon atom.

18. 4-Methyl-2-pentene

Here, the double bond between the second and third Carbon atoms in the main chain and the Methyl group is present in the fourth Carbon atom.

• In the following two compounds, a ring of three carbon atoms and three methyl groups are present at three different positions.

19. 1,2,3-Trimethylcyclopropane

Here, a ring of three carbon atoms and three Methyl groups are present in three different Carbon atoms,

20. 1,1,2-Trimethylcyclopropane

Here, a ring of three Carbon atoms with one Methyl group is present in the first and two Methyl groups are present in the second Carbon atom,

• In this compound, there is a ring of three carbon atoms and a side chain of three carbon atoms is also present.

21. Propylcyclopropane:

Here, a ring of three carbon atoms and a side chain of three carbon atoms is also present.

• In this compound, there is a ring of five carbon atoms, and one methyl group is attached to this ring.

22. Methylcyclopentane:

Here, a ring of five carbon atoms, and one methyl group is attached to this ring.

23. Isopropylcyclopropane:

Here, a ring of three carbon atoms and one Isopropyl group is attached to this ring.

• In the following two compounds, there is a ring of three carbon atoms and the position of one ethyl and methyl group varies.

24. 1-Ethyl-1-methyl cyclopropane

Here, a ring of three carbon atoms with one ethyl and methyl group is present in one carbon atom.

25. 1-Ethyl-2-methyl cyclopropane

Here, a ring of three carbon atoms with an Ethyl group is present in the first carbon atom and the Methyl group is present in the second carbon atom.

Hence, there are 25 constitutional isomers for ${\mathrm{C}}_6{\mathrm{H}}_{12}$.