Question

The pair of compounds from the following pairs having both the compounds with net non-zero dipole moment is

• A. Cis-dichloroethene; trans-dichloroethene
• B. \(CH_2Cl_2 ; CHCl_3\)
• C. 1,4-dichlorobenzene;1,3,5-trichlorobenzene
• D. Benzene; p-Anisidine

Hint:

Molecular symmetry is key to determining dipole moments. Symmetrical molecules often have zero dipole moments because individual bond dipoles can cel each other out. Asymmetrical molecules are more likely to have net dipole moments.

Answer 1

The Correct Option is B

To determine which pair of compounds from the given options have both compounds with a net non-zero dipole moment, we'll analyze each pair:

1. Cis-dichloroethene and trans-dichloroethene:

   Cis-dichloroethene has a net non-zero dipole moment because the chlorine atoms are on the same side, resulting in an asymmetric distribution of charges.

   Trans-dichloroethene, however, has a net dipole moment of zero. The chlorine atoms are on opposite sides, causing their dipole moments to cancel each other out.

   Thus, this pair does not have both compounds with non-zero dipole moments.

2. \(CH_2Cl_2\) and \(CHCl_3\):

   Both compounds have a net non-zero dipole moment.

   • \(CH_2Cl_2\) (Dichloromethane): The chlorine atoms create a significant dipole moment due to differences in electronegativity and the angular shape of the molecule.
   • \(CHCl_3\) (Chloroform): Also has a non-zero dipole moment because the asymmetric arrangement of the chlorine atoms around the central carbon atom leads to a net dipole.

   This pair satisfies the condition, so it is the correct answer.

3. 1,4-dichlorobenzene and 1,3,5-trichlorobenzene:

   1,4-dichlorobenzene has a net dipole moment of zero since the chlorine atoms are positioned para to each other, canceling their effects.

   1,3,5-trichlorobenzene, being symmetric, also has a net dipole moment of zero.

   Thus, this pair does not qualify.

4. Benzene and p-Anisidine:

   Benzene is a non-polar molecule with a net dipole moment of zero due to its symmetric structure.

   p-Anisidine has a non-zero dipole moment due to the presence of an electron-donating methoxy group opposite an amino group.

   Only one of the compounds in this pair has a non-zero dipole moment, so it does not satisfy the condition.

Therefore, the correct pair in which both compounds have a net non-zero dipole moment is \(CH_2Cl_2\) and \(CHCl_3\).