| The thesis includes two parts:Firstly, we determine the absolute configuration of several chiral molecules by comparing the calculated and experimental electronic circular dichroism (ECD) curves by using time-dependent density functional theory (TDDFT) calculations.Chirality is a property of molecules having a non-superimposable mirror image. It is one of the essential characteristics of nature. There are many chiral compounds which exist in animal, plant, medicine, food, perfume and pesticide et al. It is important to correctly determine the stereochemical structure of organic compounds for organic chemists, especially for pharmaceutical researchers. ECD is very sensitive to the spatial orientation of a chiral molecular, and it can provide optical three-dimensional structure information of chiral molecules. So it has become a powerful tool to explore the absolute configuration of molecular. ECD of chiral molecules is complicated by theoretical simulation nowadays. The method by fitting experiment data to confirm absolute configuration of chiral molecules is widely used. The most cost-effective measure to complicate ECD, found by the quantum chemical calculation, is used to simulate ECD of chiral molecules with unknown configuration. Three new absolute configuration is confirmed resulting in the solution of confirming the configuration of natural chiral molecules.At present, using TDDFT simulation to calculate the ECD of chiral molecules to determine the absolute configuration of chiral molecules has been widely used in the research of Chiral compounds. We find the most economic and effective theoretical method of calculating ECD, and apply it to simulation of chiral molecules, by fitting the experimental data, we ultimately determine the absolute configuration of three new chiral compounds which have difficulty in determining the absolute configuration under the existing conditions.The research content and conclusions are as follows:First of all, we use all kinds of theoretical calculation method, choose medium basis sets 6-31g*(6-31g* more used in the references) to simulate the ECD of Scaparvin F and compare it with experimental data, to find the accurate, time-saving computing method by the contrast analysis. Then, we calculate the ECD by different basic sets in the level of selected best theoretical calculation method,and compare it with experimental data, analyze merits and demerits to determine alternative basic sets. We simulate the natural compound found by Lou’s group which has been reported by paper and optimize our choice by comparing computation results with experimental data. Furthermore. The effect of solvation model on ECD is a very meaningful research content. So we research the effect of various solvation models in Gaussian Process (for example, PCM, CPCM, COSMO) on ECD.Conclusions as follows:The first:we try a variety of calculation methods and find B3LYP/6-31G* can provide more accurate results with more reasonable time, so we determine the best theoretical calculation method, B3LYP with 6-31g* basis sets.. In addition, optimizing the configuration in the gas and calculating single point energy in the solvent can provide better results, save time and resource.The second:we determine the absolute configurations of several new compounds.The third:using realizable method to determine the absolute configurations of aristolane sesquiterpenes, calix[4]arene crown-6 carboxylic acid.Also,we research recognition of calix[4]arene crown-6 carboxylic acid towards chiral aminoalcohols,and reveal that hydrogen bond between the gost and the guest is the primary cause of chirality. |
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