Raman Study of Hydration Effect on Conformational Equilibria of Haloacetones

The conformational equilibria of chloroacetone and bromoacetone in various solvents were investigated using temperature and pressure-tuning Raman spectroscopy. Three conformational equilibria of gauche (left arrow)(right arrow) trans, gauche (left arrow)(right arrow) transʹ (trans conformer whose halogen atom forms hydrogen bonds with water), and trans (left arrow)(right arrow) transʹ were observed in water. Thermodynamic quantities between the conformers of both haloacetones in various solvents were evaluated from the temperature and pressure dependence of the Raman intensities of the C-X (X: Cl and Br) stretching modes. The effects of the substitution of halogen atoms were observed in the enthalpy and volume differences between the conformers in water. From the present results together with the previous results for fluoroacetone, a good correlation between the conformational thermodynamics for haloacetones in water and the polarizabilities of the halogen atoms was shown.