Question

Which from following molecules exhibits lowest dipole moment?

• A. CH3F
• B. CH3Cl
• C. CH3Br
• D. CH3I

Answer 1

Answer: (D)

CH₃I

Answer 2

The dipole moment in these molecules arises primarily from the C–X (X = halogen) bond. Although the bond length increases from F to I, the electronegativity difference between carbon and the halogen decreases. In CH₃F, despite a short bond length, the large electronegativity difference gives a significant dipole moment. In CH₃Cl, the longer bond length overcompensates its lower electronegativity difference, leading to the maximum dipole moment (as given in the similar question). Moving further to CH₃Br and CH₃I, the difference in electronegativity further decreases, resulting in even lower bond dipoles. Hence, CH₃I, with the lowest electronegativity difference and a very long bond, exhibits the lowest dipole moment.