Draw the structural isomers of \(\mathrm{C}_{4} \mathrm{H}_{9} \mathrm{Cl}\) in which one hydrogen atom of a \(\mathrm{C}_{4} \mathrm{H}_{10}\) molecule has been replaced by chlorine.

Structural isomers are compounds with the same molecular formula but different arrangements of atoms. In this exercise, we will be focusing on the structural isomers of C4H9Cl that can be formed by replacing a hydrogen atom of a C4H10 molecule with a chlorine atom.

Before we can replace a hydrogen atom with a chlorine atom, we need to know the different structures that a C4H10 molecule can have. There are two possible structures for C4H10: 1. n-butane: a linear arrangement of four carbon atoms, with each carbon atom bonded to its neighboring carbon atoms and hydrogen atoms to complete the valency. The structure is as follows: \(\displaystyle \mathrm{H}_{3} \mathrm{C}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{3}\) 2. Isobutane: a branched arrangement, with three carbon atoms bonded linearly and the fourth carbon atom bonded to the central carbon atom. It is represented as: \(\displaystyle \mathrm{H}_{3} \mathrm{C}-\mathrm{CH}\left(\mathrm{CH}_{3}\right)-\mathrm{CH}_{3}\)

Now, we will replace one hydrogen atom of the C4H10 structures with a chlorine atom, creating the structural isomers of C4H9Cl. 1. For n-butane, there are two possible isomers: a. 1-chlorobutane: Replace a hydrogen atom on the first carbon atom: \(\displaystyle \mathrm{ClCH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}_{3}\) b. 2-chlorobutane: Replace a hydrogen atom on the second carbon atom: \(\displaystyle \mathrm{H}_{3} \mathrm{C}-\mathrm{CH}\left(\mathrm{Cl}\right)-\mathrm{CH}_{2}-\mathrm{CH}_{3}\) 2. For isobutane, there is only one possible isomer: c. 2-chloro-2-methylpropane: Replace a hydrogen atom on the second carbon atom (attached to the methyl group): \(\displaystyle \mathrm{H}_{3} \mathrm{C}-\mathrm{C}\left(\mathrm{Cl}\right)-\left(\mathrm{CH}_{3}\right)-\mathrm{CH}_{3}\)

In this exercise, we have found three structural isomers of C4H9Cl, formed by replacing a hydrogen atom of C4H10 with a chlorine atom. The three isomers are: 1-chlorobutane, 2-chlorobutane, and 2-chloro-2-methylpropane.