Among the chloromethanes, the experimental dipole moments do not follow a simple monotonic trend rel — Haloalkanes and Haloarenes Chemistry Question

💡 Solution & Explanation

The correct order of dipole moments is $CH_3Cl$ ($1.86$ D) $> CH_2Cl_2$ ($1.60$ D) $> CHCl_3$ ($1.03$ D) $> CCl_4$ ($0$ D). As the number of $C-Cl$ bonds increases, their individual bond dipoles point towards the corners of a tetrahedron. In $CH_3Cl$, the $C-Cl$ dipole is strongly reinforced by the small $C-H$ dipoles. In $CH_2Cl_2$, the vector sum of two $C-Cl$ bonds is smaller than the single prominent axis in $CH_3Cl$. In $CHCl_3$, three $C-Cl$ dipoles heavily oppose each other, yielding an even smaller net dipole. Finally, $CCl_4$ is perfectly symmetrical, causing total vector cancellation.