Which of the following molecules has the highest dipole moment: $1,2,4,5\text{-tetrachlorobenzene}$, $1,2,3,4\text{-tetrachlorobenzene}$, $1,2,3,5\text{-tetrachlorobenzene}$, or $1,2,4,5\text{-tetrachlorobenzene}$?

Solution

1. Dipole moment is a vector quantity determined by molecular geometry and symmetry.
2. $1,2,4,5\text{-tetrachlorobenzene}$ has a center of inversion and a dipole moment of zero.
3. $1,2,3,4\text{-tetrachlorobenzene}$ has a lower symmetry and a small net dipole.
4. $1,2,3,5\text{-tetrachlorobenzene}$ has a highly asymmetric arrangement of chlorine atoms leading to a large net dipole.
5. Hence the answer is (C).