= Solution
\b[The gas-phase attraction is a <cation–π interaction>.] The positively charged ion interacts with benzene's electron distribution and polarizes the aromatic molecule. An orientation above the ring face allows stabilization without a conventional covalent bond. A modest association constant reflects the balance of that attraction against the entropy cost of joining two independent species, at the stated gas-phase standard state.
In water, a small ion such as $\mathrm{Li^+}$ is strongly solvated. Forming a direct benzene complex requires rearranging or losing favourable ion–water contacts; benzene is also solvated, and the solvent screens electrostatic interactions. The relevant solution free energy therefore includes \b[desolvation and solvent reorganization], not just the attractive energy of the isolated pair. The gas-phase association constant cannot be transferred to water without changing this thermodynamic cycle and the standard states. The interaction is not forbidden in solution, but it need not give appreciable direct complexation under the specified conditions.
Back to article page
