Question

Which of the set of isomers of $C_6{H}_{4}C{l}_2$ is having equal dipole moment with $C_6{H}_{5}Cl$ and $C_6{H}_6$ respectively?

• A. Ortho and Meta
• B. Meta and Para
• C. Ortho and Para
• D. Para and Ortho

Answer 1

The correct option is B Meta and Para

The expression for dipole moment is ${\mu }_R=\sqrt{{\mu }_1^2+{\mu }_2^2+2{\mu }_1{\mu }_{2}cos\theta }$
In case of meta dichloro benzene, the bond angle between two carbon chlorine bonds is ${120}^o$. Hence, $cos\theta =cos120=-0.5$ and ${\mu }_1={\mu }_2={\mu }_R$.
Hence, the dipole moment of meta dichlorobenzene is equal to that of chlorobenzene.
In case of para dichlorobenzene, the bond angle between two carbon chlorine bonds is ${180}^o$. Hence, $cos\theta =cos180=-1$ and ${\mu }_R=0$.
Hence, the dipole moment of para dichlorobenzene is equal to that of benzene.