Ethyl Acetoacetate Proton Transfer Process And The Spectrum Of Theoretical Research

As one of the simplest and most basic phenomenon in the isomerization balance andredox reaction, proton transfer (PT) in intra- and inter- molecule plays an importantrole in many chemical processes. Hydrogen bond formation and proton transferphenomena in many chemical processes are very important and common, protontransfer can progress through the hydrogen bonds form between organic molecules.Such transfer is also important with energy transfer and electronic transfer inmolecular system, almost all organic reactions have included all or part of the protontransfer process. Proton transfer plays an important role in the transmission ofinformation between molecules. This paper chose ethyl acetoacetate as a investigateobject, and we researched the proton transfer processes of its monomer, dimmer andmonohydrate in the ground and excited states. The most stable structure and the mostpossible reaction path were found. Furthermore, their spectrums also have beenstudied. The main contents of the paper contain 3 parts, just as follows:1. Density functional theory (DFT) of quantum chemistry method is used tostudy proton transfer reaction of ethyl acetoacetate monomer, dimer and thewater-assisted process in the ground state. By studying the potential energy curves ofthe isomerization, the most possible reaction pathway was found. The results showthat ethyl acetoacetate both monomer and dimer, or a hydrate. The energy of ketoform is a little lower than enol form, which shows that under normal circumstancesethyl acetoacetate exist as both keto form and enol form, keto form is the main part.The studies of three possible reaction mechanism show direct proton transfer processhas the high activation energy(255.7kJ·mol^-1, 220.7 kJ·mol^-1), the activation energy ofdimer two-proton transfer between molecules is reduced 48.3 kJ·mol^-1, when thewater is as a catalyst, the activation energy is reduced 29.4 kJ.mol^-1 and 103 kJ·mol^-1,the reaction is even easier. The results also show hydrogen bond plays a veryimportant role in depressing the activation energy of reaction. The mechanism of thetautomerization was discussed on the basis of theoretical results.2. Apply the same configuration of the CIS optimization ethyl acetoacetatemonomer, dimer and a hydrate structure of the excited states. The results show thatthe monomer and dimer in the excited state proton transfer process was essentially thesame, As the activation energy of proton transfer reaction from keto form to enol form in excited state is great, the reaction is difficult to occur. The activation energy ofinverse reaction is relatively low, the reaction can happen. And because enol formmostly becomes keto form, the later is stabile in excited state. We calculated the UVabsorption spectrum datas which were in good agreement with experimental results byhybrid time-dependent density functional theory (TD/B3LYP) method with theexistence of solvent, both ground and excited states of its monohydrate constitute afour-state cycle, the keno form of monohydrate is more stabile than enol form in theground state. Because the activation energy of proton transfer reaction from keto formto enol form in excited state is great, the reaction is difficult to occur.3. The DFT TD/MPW1PW91 and time-dependent density functional theoryTD/DFT, at 6-311+G^*-based set, cyclohexene as a solvent, is used to calculate UVabsorption spectroscopy of the ethyl acetoacetate monomer and dimer. The resultsshow the keno form M1 and enol form M2 of the monomer in the ground state arestable. As the positive and inverse activation energy of proton transfer reaction fromketo form to enol form in excited state is very high, the reaction is difficult to occur.So monomer UV absorption spectra is corresponding to both keto and enol form.