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

1. cis-Butene vs. trans-Butene

• cis-Butene: Has a non-zero dipole moment due to the asymmetrical placement of methyl groups on the same side of the double bond.
• trans-Butene: Has a zero dipole moment because the methyl groups are on opposite sides, resulting in a symmetrical arrangement and cancellation of bond dipoles.

2. Benzene vs. Anisidine

• Benzene: Has a zero dipole moment due to its symmetrical structure.
• Anisidine (Methoxybenzene): Has a non-zero dipole moment due to the electron-donating methoxy group (-OCH₃), which causes an uneven charge distribution.

3. CH₂Cl₂ vs. CHCl₃

• CH₂Cl₂ (Dichloromethane): Has a non-zero dipole moment due to the electronegativity difference between carbon and chlorine, combined with its asymmetrical structure.
• CHCl₃ (Chloroform): Also has a non-zero dipole moment for the same reasons as CH₂Cl₂, with an asymmetrical distribution of bond dipoles.

4. 1,4-Dichlorobenzene vs. 1,3-Dichlorobenzene

• 1,4-Dichlorobenzene (para-Dichlorobenzene): Has a zero dipole moment due to its symmetrical structure, where the C-Cl bond dipoles cancel each other out.
• 1,3-Dichlorobenzene (meta-Dichlorobenzene): Has a non-zero dipole moment because the C-Cl bond dipoles do not completely cancel each other out, resulting in an asymmetrical charge distribution.

Conclusion:

• Molecules with symmetrical structures typically have zero dipole moments.
• Molecules with asymmetrical structures or electron-donating/withdrawing groups usually have non-zero dipole moments.