Conformational stability, molecular structure, and intramolecular hydrogen bonding of thenoyltrifluoroacetone

Complete conformational analysis of all possible keto and enol forms of thenoyltrifluoroacetone (TTFA) was carried out using density functional theory with the B3LYP functional and the 6-31G**, 6-311G**, and 6-311++G** basis sets. In addition, the geometries and energies of the four most stable chelated conformers and their corresponding open structures were obtained at the MP2/6-31G** level of theory. The energy differences between the four stable chelated enol conformers, in the gas phase, calculated at the B3LYP levels are negligible. However, calculations at the MP2 level indicate that the B2 conformer (the hydroxyl group in the -CF3 side) is significantly more stable than others, in agreement with the X-ray diffraction results. The calculated intramolecular hydrogen bond (IHB) energy E-HB and the strength of the bond have been compared, and an imperfection in the prevalent method of evaluating E-HB has been perceived. The IHB of TTFA was compared with those in several beta-dicarbonyls.