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The Study on Vibrational Spectra of Correlative Organic Ester Compounds in the Chinese Famous Liquor

Author: CaiZhiPeng
Tutor: MoYuJun
School: Henan University
Course: Optics
Keywords: Ethyl acetate ethyl lactate ethyl hexanoate MMA organic ester compounds DFT Raman IR Surface Enhanced Raman Scattering(SERS)
CLC: TS261
Type: Master's thesis
Year: 2007
Downloads: 160
Quote: 2
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Abstract


Ethyl acetate, ethyl lactate and ethyl hexanoate are three most important organic ester compounds in the Chinese famous liquor, distinction of their contents and proporsition determine the flavor of the Chinese famous liquor. More, as an important chemistry industry material, this three organic ester compounds have a wide applications.Ethyl acetate is one of the most extensive fatty acid ester in application. It is an important fine chemical industry material, and is an important solvent, extractant and food additive. It finds its great application in the field of paint, printing ink, artificial leather, artificial essence, cellulose nitrate, bonder and medicine as an important fine chemical industry material, solvent, extractant and food additive. Ethyl lactate is a water soluble compound and is of valuable application in fields of food, medicine, paint and research. Ethyl hexanoate is an organic ester compound flavor; which is widely used in food flavouring aspect. Mainly, it is used in flavor of wine, vineger and candy.In addition, for the study of surface enhanced Raman scattering (SERS) property on above three organic ester compounds, we study another organic ester compounds methyl methacrylate(MMA). As for an important organic chemistry industry material, methyl methacrylate is mainly used to synthesize PMMA(polymethyl methacrylate) besides its application in the production of other polymer, such as plastics, paint, bonder and lubricant additives.Density Functional Theory (DFT) method is widely used to calculate molecular vibration spectrum by means of the method based on approximately energy density function. Contrasting with Hartree-Fock, DFT method can calculate larger complex matrix with the merit of smaller calculation amounts. DFT method considers the electron exchange and electron correlation energy in the process of calculation, so the calculated results are more precise than other theories.As important analytical instruments, Raman and infrared spectra have been widely used in the molecular structure research, and they take significant status in physics and chemistry studies nowadays. SERS has high surface and interface susceptivity and detective sensitivity, which is a kind of good surface analytical instrument and has broad applications.This thesis is divided into three parts as follows:The first chapter introduces trace components in liquor, classification of Chinese famous liquor flavor styles and methods of distinguishing liquor at present. It also narrates applications and recent progress on the study of the three most important organic ester compounds in the Chinese famous liquor.The second chapter introduces Raman and infrared spectra of ethyl acetate, ethyl lactate and ethyl hexanoate. On the base of the vibrational spectra of ethyl acetate, ethyl lactate and ethyl hexanoate calculated by the Density Functional Theory (DFT), the normal Raman and the infrared spectra are assigned in detail. The reason for the appearance of ethyl lactate and ethyl hexanoate peaks in the experimental Raman and infrared specra but not in the calculated vibrational spectra is interpreted reasonablely. It is also found that C=O band of ethyl lactate is inclined to form weak hydrogen bond but not a strong one. The Raman and infrared adsorption spectra of methyl methacrylate(MMA) is discussed the third chapter, compared with DFT calculated result, the vibrational modes about methyl methacrylate are consequently assigned. Meanwhile, for disposing of impure on the surface silver mirror, the method that SERS substrate are soaked in KCl solution is used, which do not reduce SERS result of the substrate, accordingly, the mechanism of the process is analyzed. The adsorption behavior of the molecule on silver mirror SERS substrate is studied, and we draw a conclusion that methyl methacrylate molecular is adsorbed on the substrate by the C=C band, not by C=O band, which might show very poor or no interaction between C=O band and substrate. Repeated experimental results show that ethyl acetate, ethyl lactate and ethyl hexanoate have very poor or no SERS effect, and possible reasons of this phenomenon are discussed compared with absorption of methyl methacrylate on substrate. In the end, we bring up several possible methods for the detection of the three important organic ester compounds, from which the SERS signal of them could be observed.

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