Question

What are the chain isomers of ${{\text{C}}_4}{{\text{H}}_{10}}$

Answer 1

An isomer is a molecule with the same molecular formula but different arrangements of atoms or different structures. They may have different physical and chemical properties. Isomers can be classified into 2, which are constitutional isomers and stereoisomers. Constitutional isomers are also called structural isomers. It includes chain isomers, position isomers, functional group isomers. When the same molecule shows different branching patterns, it is called chain isomers.

Complete step by step answer:
The molecule given here is ${{\text{C}}_4}{{\text{H}}_{10}}$
It has 4 Carbon atoms and 6 Hydrogen atoms. So we can say that it is a saturated molecule.
Now let us draw the structure of the parent chain ${{\text{C}}_4}{{\text{H}}_{10}}$
${\text{C}}{{\text{H}}_{\text{3}}}{\text{--C}}{{\text{H}}_{\text{2}}}{\text{--C}}{{\text{H}}_{\text{2}}}{\text{--C}}{{\text{H}}_{\text{3}}}$
This is the parent chain ${{\text{C}}_4}{{\text{H}}_{10}}$. Its IUPAC name is n-butane.
Now we need to find the chain isomers. For that, different branching patterns can be done.
${\text{C}}{{\text{H}}_{\text{3}}}{\text{--CH(C}}{{\text{H}}_{\text{3}}}{\text{)--C}}{{\text{H}}_{\text{3}}}$ in which one of the ${\text{C}}{{\text{H}}_{\text{3}}}$ groups from the parent chain is attached to the second carbon atom. It still has got 4 Carbon and 10 Hydrogen. So it’s a branch chain isomer of ${{\text{C}}_4}{{\text{H}}_{10}}$. It is named as 2-methyl propane. We can see here that it is a secondary alkane as the ${\text{C}}{{\text{H}}_{\text{3}}}$ attached Carbon has only 1 hydrogen and it is ${\text{s}}{{\text{p}}^{\text{2}}}$ hybridized.
There are no more chain isomers possible for this molecule.
Therefore, the number of chain isomers of ${{\text{C}}_4}{{\text{H}}_{10}}$ is 2.
Thus, the correct answer is 2.

Note: To find whether it is saturated or unsaturated, you may also use the formula ${{\text{C}}_{\text{n}}}{{\text{H}}_{{\text{2n + 2}}}}$. If the given molecular formula holds good for this formula, it means that the given compound is saturated or it is an alkane. In this case, there were only 2 chain isomers. When it comes to molecules like pentane ${{\text{C}}_{\text{5}}}{{\text{H}}_{{\text{12}}}}$, there can be more chain isomers like n-pentane, 2-methyl butane, 3-methyl butane, 2,2-dimethylpropane.