The effect of pressure on the conformational equilibrium of chloroacetone in carbon disulfide was measured using a high pressure infrared spectroscopy with a diamond anvil cell at the region of C=O and Cndash;Cl stretching vibrational bands up to 12 kbar. The observed frequencies of theC=O stretching vibration decreased with increasing pressure by minus;0.56 cmminus;1thinsp;kbarminus;1for the higher frequency bands and minus;0.47 cmminus;1thinsp;kbarminus;1for the lower frequency bands. The frequencies of Cndash;Cl bands at 6 kbar increased by 0.33 cmminus;1thinsp;kbarminus;1for the higher frequency and 0.57 cmminus;1thinsp;kbarminus;1for the lower frequency. The pressure effects on the frequency shift were discussed with respect to Bauer and Magatrsquo;s theory of solvent shift and intermolecular forces. The volume changes for the transformation from the conformer assigned to the lower frequency to the conformer assigned to the higher frequency were determined to be minus;1.6plusmn;0.1 cm3thinsp;molminus;1for Cndash;Cl band and minus;1.5plusmn;0.2 cm3thinsp;molminus;1for C=O band. These observed volume changes were considered to be the result of three possible factors: the intrinsic volume difference between isomers which is 0.66 cm3thinsp;molminus;1; the packing effect of the solute and solvent, 0 to minus;1.8 cm3thinsp;molminus;1; and the solvent effect, minus;3.0 cm3thinsp;molminus;1. From the pressure dependence of the frequency shifts of the C=O and Cndash;Cl stretching vibrations and the volume changes for the conformational isomerism, it is clear that the lower frequency bands are assigned to the less polar form and the higher frequency bands to the more polar form.
展开▼
