JEE Main · 2006 · 30 Apr 2006 · Offline · Chemical Bonding and Molecular Structure

Dipole-dipole forces dominate only when both partners are polar yet neither offers strong hydrogen bonding or an ionic interaction. A benzene-ethanol mixture is ruled by hydrogen bonding from the alcohol, $\mathrm{KCl}$ in water by ion-dipole attraction, and benzene with $\mathrm{CC}{\mathrm{l}}_4$ by London dispersion since both are non-polar. In the mixture of acetonitrile, $\mathrm{C}{\mathrm{H}}_3\mathrm{CN}$, and acetone, $\mathrm{C}{\mathrm{H}}_3\mathrm{COC}{\mathrm{H}}_3$, both molecules are polar but neither has an $\mathrm{O}-\mathrm{H}$ or $\mathrm{N}-\mathrm{H}$ for hydrogen bonding, so dipole-dipole attraction is the major interaction there.