Chemistry - CHEMICAL BONDING Question with Solution | TestHub

$\underset{1.64\mathrm{D}}{\mathrm{C}{\mathrm{H}}_3\mathrm{I}}<\underset{1.79\mathrm{D}}{\mathrm{C}{\mathrm{H}}_3\mathrm{B}\mathrm{r}}<\underset{1.84\mathrm{D}}{\mathrm{C}{\mathrm{H}}_3\mathrm{F}}<\underset{1.94\mathrm{D}}{\mathrm{C}{\mathrm{H}}_3\mathrm{C}\mathrm{l}}$
The charge separation in$\mathrm{C}-\mathrm{X}$bond decreases in the order
$\mathrm{C}-\mathrm{F}>\mathrm{C}-\mathrm{C}\mathrm{l}>\mathrm{C}-\mathrm{B}\mathrm{r}>\mathrm{C}-\mathrm{I},$due to decrease in the electronegativity as we more from$\mathrm{F}\to \mathrm{C}\mathrm{l}\to \mathrm{B}\mathrm{r}\to \mathrm{I}$.
$\mathrm{C}{\mathrm{H}}_3\mathrm{C}\mathrm{l}$has higher dipole moment than$\mathrm{C}{\mathrm{H}}_3\mathrm{F}$, because of larger bond length of$\mathrm{C}-\mathrm{C}\mathrm{l}$bond. The larger$\mathrm{C}-\mathrm{C}\mathrm{l}$bond length causes dipole moment$\left(\mathrm{\mu }\right)=\mathrm{q}\times \mathrm{d}$to be larger for$\mathrm{C}{\mathrm{H}}_3\mathrm{C}\mathrm{l}$than$\mathrm{C}{\mathrm{H}}_3\mathrm{F}$. In case of other haloalkanes, the effect of larger$\mathrm{C}-\mathrm{X}$bond length cannot outweigh the effect of decreased charge separation.