Question

Which of the following will have the maximum Dipole Moment?

• A. ${\mathrm{CH}}_3\mathrm{I}$
• B. ${\mathrm{CH}}_3\mathrm{F}$
• C. ${\mathrm{CH}}_3\mathrm{Br}$
• D. ${\mathrm{CH}}_3\mathrm{Cl}$

Answer 1

The correct option is D

${\mathrm{CH}}_3\mathrm{Cl}$

Explanation for correct option:

D. ${\mathrm{CH}}_3\mathrm{Cl}$

Dipole moment:

• “Dipole moment is defined as the product of the magnitude of the charge and the distance between the centers of positive and negative charge”
• It is expressed as $\left(\mathrm{\mu }\right)$.

The trend for dipole moment in the case of halogens are:

• Dipole moment depends on charge and distance.
• The difference in electronegativity between carbon and halogen atom decreases on going down the group from Fluorine to Iodine because of the decrease in electronegativity of halogen down the group.
• On the other hand, the distance between carbon and halogen atom increases on going down the group from Fluorine to Iodine because of the increase in size on moving down the group in the halogen family.
• The dipole moment of ${\mathrm{CH}}_3\mathrm{Cl}$ is greater than that of ${\mathrm{CH}}_3\mathrm{F}$ as the electron affinity of chlorine is greater than that of fluorine. The charge separation is larger in ${\mathrm{CH}}_3\mathrm{Cl}$ compared to ${\mathrm{CH}}_3\mathrm{F}$. The repulsion between the bond pairs and non–bonded pairs of electrons is greater in ${\mathrm{CH}}_3\mathrm{Cl}$ than ${\mathrm{CH}}_3\mathrm{F}$.
• Thus, the charge and distance factors are opposite to each other, in this case, the charge factor dominates. Therefore, the order will be $\text{C}{\text{H}}_3\text{Cl}>\text{C}{\text{H}}_3\text{F}>\text{C}{\text{H}}_3\text{Br}>\text{C}{\text{H}}_3\text{I}$.

Explanation for incorrect options:

The order of the dipole moment is $\text{C}{\text{H}}_3\text{Cl}>\text{C}{\text{H}}_3\text{F}>\text{C}{\text{H}}_3\text{Br}>\text{C}{\text{H}}_3\text{I}$. Thus, ${\mathrm{CH}}_3\mathrm{Cl}$ will have the maximum dipole moment. Therefore, options A, B, and C are incorrect.

Hence, the correct option is D i.e. ${\mathrm{CH}}_3\mathrm{Cl}$.