Question

Which has the highest dipole moment and give the order ${\mathrm{CH}}_3\mathrm{Cl},{\mathrm{CH}}_2{\mathrm{Cl}}_2,{\mathrm{CHCl}}_3\mathrm{or}{\mathrm{CCl}}_4$

Answer 1

Dipole moment:-

• The measurement of the polarity of the chemical bond in a molecule between 2 atoms is called the Dipole moment.
• In Methyl chloride$\left({\mathrm{CH}}_3\mathrm{Cl}\right)$, there are 3 $\mathrm{C}-\mathrm{H}$bonds and 1 $\mathrm{C}-\mathrm{Cl}$bond.
• The chlorine here is more electronegative than carbon, and thus the result of the 3 $\mathrm{C}-\mathrm{H}$ dipole bond is reduced by the single $\mathrm{C}-\mathrm{Cl}$ dipole bond.
• Thus it has the highest dipole moment amongst the others

• In ${\mathrm{CH}}_2{\mathrm{Cl}}_2$, there are 2 $\mathrm{C}-\mathrm{H}$bonds and 2 $\mathrm{C}-\mathrm{Cl}$bonds.
• Here the resultant of the 2 $\mathrm{C}-\mathrm{H}$ dipole bonds are reduced by the 2 $\mathrm{C}-\mathrm{Cl}$ dipole bond.
• This results in less dipole moment of ${\mathrm{CH}}_2{\mathrm{Cl}}_2$than $\left({\mathrm{CH}}_3\mathrm{Cl}\right)$.

• Like this in a similar fashion, the dipole moment of ${\mathrm{CHCl}}_3$ is also lower than ${\mathrm{CH}}_2{\mathrm{Cl}}_2$ and also $\left({\mathrm{CH}}_3\mathrm{Cl}\right)$.

• In ${\mathrm{CCl}}_4$, there are 4 $\mathrm{C}-\mathrm{Cl}$ bonds and thus the dipole moment is 0.
• This is because, the 4 $\mathrm{C}-\mathrm{Cl}$ dipole bonds cancel each other out, as the angle between the trans position of the Cl atom is $180°$.
• Hence it has the least dipole moment amongst the others.

Therefore, the correct decreasing order of dipole moment is ${\mathrm{CH}}_3\mathrm{Cl}>{\mathrm{CH}}_2{\mathrm{Cl}}_2>{\mathrm{CHCl}}_3>{\mathrm{CCl}}_4$