Question

Arrange the following compounds in increasing dipole moment: toluene (I), $m$-chlorobenzene (II), $o$ dichlorobenzene (III), $p$-dichlorobenzene (IV)

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

Answer 1

Answer: (B)

$\mu =2{\mu }_{C-X}\cos \left(\frac{\theta }{2}\right)$
$\mu \propto \cos \left(\frac{\theta }{2}\right)$
$\mu \propto \frac{1}{\theta }$ (since as $\theta$ increases, $\cos \theta$ decreases)
Thus, ${\mu }_{IV}=0\left(\cos \frac{180^{\circ }}{2}=\cos 90^{\circ }=0\right)$
and order being