The dipole moment of a violet solution of iodine in cyclohexane is zero. When benzene, dioxane or pyridine is added to it, its colour changes and the dipole moment of `I_(2)` in the presence of these solvents becomes 1.8, 3.0 and 4.5D, respectively. Explain.

Explanation

Iodine forms charge transfer complexes with donor solvent molecules. Cyclohexane with no unshared electron pair does not form a charge transfer complex with `I_(2)` . But donor molecules like benzene, dioxane and pyridine form charge transfer complexes with `I_(2)`. Since donor strength increases in the order of benzene `lt`dioxane `lt` pyridine , the tendency of electron transfer increases in the same order. Hence, dipole moment increase as: benzene `cdotI_(2)`(1.8D)`lt` dioxane `cdotI_(2)(3.0D)lt` pyridine `cdotI_(2)` (4.5D).