When analyzing the series of polyhalogenated methanes, why does the net dipole moment decrease drama — Haloalkanes and Haloarenes Chemistry Question

💡 Solution & Explanation

Dipole moment is a vector quantity. While chloroform ($CHCl_3$) has three highly polar $C-Cl$ bonds, the molecule assumes a tetrahedral geometry. The three $C-Cl$ bond vectors point away from the central carbon toward the base of a trigonal pyramid. Because they are spread out radially, their horizontal vector components effectively cancel each other out, leaving only a modest resultant vector pointing down the axis. In contrast, in chloromethane ($CH_3Cl$), the single large $C-Cl$ vector is unopposed by other halogens and is actually reinforced by the three small $C-H$ bond dipoles pushing in the same general direction, resulting in a much larger net dipole moment.