Question

What is the number of possible structural isomers for bromopentane ?
A) ${\text{1}}$
B) ${\text{3}}$
C) ${\text{6}}$
D) ${\text{8}}$

Answer 1

Hint: The structural isomers are the compounds that have the same molecular formula but they differ in their arrangement of atoms or groups in the molecule. One can draw the basic structure and see for possible structural isomers for better interpretation of isomers.

Complete step by step answer:
1) First of all let's write the general molecular formula for the bromopentane which is ${C_5}{H_{11}}Br$. The structural isomers for the bromopentane are as follows,
The first possible structural isomer for the bromopentane is ${\text{1 - }}$bromopentane which has the bromine atom attached to the first carbon atom. The structure is as follows,
$Br - C{H_2} - C{H_2} - C{H_2} - C{H_2} - C{H_3}$
The second possible structural isomer for the bromopentane is ${\text{2 - }}$bromopentane which has the bromine atom attached to the second carbon atom. The structure is as follows,
$C{H_3} - C{H_2}(Br) - C{H_2} - C{H_2} - C{H_3}$
The third possible structural isomer for the bromopentane is ${\text{3 - }}$bromopentane which has the bromine atom attached to the third carbon atom. The structure is as follows,
$C{H_3} - C{H_2} - CH(Br) - C{H_2} - C{H_3}$
The fourth possible structural isomer for the bromopentane is ${\text{1 - }}$bromo${\text{ - 3 - }}$methylbutane which has the bromine atom attached to the first carbon atom and methyl group to the third carbon atom. The structure is as follows,
$Br - C{H_2} - C{H_2} - CH(C{H_3}) - C{H_3}$
The fifth possible structural isomer for the bromopentane is ${\text{2 - }}$bromo${\text{ - 3 - }}$methylbutane which has the bromine atom attached to the second carbon atom and methyl group to the third carbon atom. The structure is as follows,
$C{H_3} - CH(Br) - CH(C{H_3}) - C{H_3}$
The sixth possible structural isomer for the bromopentane is ${\text{2 - }}$bromo${\text{ - 2 - }}$methylbutane which has the bromine atom attached to the second carbon atom and methyl group to the second carbon atom. The structure is as follows,
$C{H_3} - (Br)C(C{H_3}) - C{H_2} - C{H_3}$
The seventh possible structural isomer for the bromopentane is ${\text{1 - }}$bromo${\text{ - 1 - }}$methylbutane which has the bromine atom attached to the first carbon atom and methyl group to the first carbon atom. The structure is as follows,
$(Br)C(C{H_3}) - C{H_2} - C{H_2} - C{H_3}$
The eighth possible structural isomer for the bromopentane is ${\text{1 - }}$bromo${\text{ - 2,2 - }}$dimethylpentane which has the bromine atom attached to the first carbon atom and two methyl groups to the second carbon atom. The structure is as follows,
${(C{H_3})_3}C - C{H_2} - Br$
Therefore, the structure of bromopentane shows eight structural isomers which show the option D as a correct choice.

Therefore, option D is the correct choice.


Note:
While writing the structural isomers one should always remember to fulfill the valency of a carbon atom which is four. Each structural isomer has different chemical and physical properties than other isomers but they all have the same molecular formula.