The dipole moment of fluoromethane ( D) is unexpectedly lower than that of chloromethane ( D), even — Haloalkanes and Haloarenes Chemistry Question

💡 Solution & Explanation

Dipole moment ($\mu$) is the product of the magnitude of partial charge ($q$) and the distance of separation or bond length ($d$), i.e., $\mu = q \times d$. While fluorine is more electronegative and creates a larger partial charge ($q$) on the carbon atom, the $C-Cl$ bond distance ($178$ pm) is considerably larger than the $C-F$ bond distance ($139$ pm). The proportional increase in the bond distance ($d$) from fluorine to chlorine slightly overcompensates for the decrease in charge ($q$), resulting in chloromethane having a marginally higher overall dipole moment.