Question

Arrange the following compounds in order of increasing dipole moment.
Toluene $\left(I\right)$, m-dichlorobenzene$\left(II\right)$, o-dichlorobenzene$\left(III\right)$, p-dichlorobenzene$\left(IV\right)$.

• A. $I<IV<II<III$
• B. $IV<I<II<III$
• C. $IV<I<III<II$
• D. $IV<II<I<III$

Answer 1

The correct option is B $IV<I<II<III$

Dipole moment of p-dichlorobenzene is zero because of symmetrical structure. o- and m-dichlorobenzene have higher dipole moments than toluene due to high electronegativity of chlorine than $-C{H}_3$ group. Further, the o-dichlorobenzene has higher dipole moment due to lower bond angle than the m-isomer. Hence, the order of increasing dipole moment is:
p-dichlorobenzene $\left(IV\right)$ < toluene $\left(I\right)$ < m-dichlorobenzene $\left(II\right)$ < o-dichlorobenzene $\left(III\right)$.