| Summary: | 碩士 === 中原大學 === 化學研究所 === 106 === The fascinating tautomerization process involving hydrogen migration of acetylacetone (denoted as Acac) has drawing much research attention over the past years. This microscopic molecular level tautomerization process will result in the macroscopic ensemble Keto‒to‒Enol equilibrium. In order to have a global understanding of the Acac tautomerization, the nuclear magnetic resonance (NMR) technology was used on both the microscopic electron cloud investigation (such as chemical shift observation) and the macroscopic ensemble average phenomenon of spectra themself. Thermodynamically, the Keto‒to‒Enol interstructural conversion of Acac is essentially an enthalpy-controlled mechanism. Besides the relatively fixed bond energy and conjugated resonance energy, the intramolecular hydrogen bonding of Acac plays a key role in the Acac’s Enol/Keto ratio. A series of multinuclear 1H, 2D, 13C, 17O and diffusion experiments in different solvents, temperatures, and concentrations were performed. Experimental results show that the Keto to Enol ratio of pure Acac is roughly 1 : 4. The main factor that affects Acac’s Enol/Keto ratio is the intramolecular hydrogen bond strength of the Enol structure. A higher temperature is thus more favorable to the Keto form structure. A lower dielectric constant solvent has less effect on the intramolecular hydrogen bond strength and therefore favors the Enol tautomer. Protic solvents, such as water, will quickly and completely destroy the intramolecular hydrogen bonding and cause the Acac to have more Keto molecules than its Enol molecules.
|
|---|
