The intrinsic crystal lattice enthalpy strictly dictates the melting point of solid aromatic halogen — Haloalkanes and Haloarenes Chemistry Question
Question
The intrinsic crystal lattice enthalpy strictly dictates the melting point of solid aromatic halogen derivatives. When systematically evaluating and comparing the isomeric derivatives of dichlorobenzene, which of the following advanced statements are physically true?
💡 Solution & Explanation
All statements correctly describe the interplay of molecular geometry and intermolecular forces. A) The $180^\circ$ symmetry of the $p$ -isomer allows perfect, dense stacking in a lattice. B) Dense stacking equals high lattice enthalpy, driving up the melting point. C) Once melted, boiling point depends on liquid-phase attractions. The $p$ -isomer has $\mu = 0$, so it relies solely on London dispersion forces, giving it the lowest BP ($170^\circ C$) compared to $o$ - ($181^\circ C$) and $m$ - ($173^\circ C$). D) The $m$ -isomer's $120^\circ$ angle creates the most awkward shape for efficient packing, giving it the lowest MP ($-25^\circ C$) compared to $o$ - ($-17^\circ C$).