Study On Graph The Oretical Representation Of Chirality Of Benzenoids In Two-dimensional Space

(1) Study on2D molecular chiralityIn order to explore atomic asymmetry and molecular chirality in2D space, benzenoids composed of3to11benzene rings in2D space were enumerated in this research. These benzenoids are regarded as planar connected polyhexes and have no internal holes, that is, their internal regions are filled with hexagons. The produced dataset was composed of357968benzenoids, including more than14million atoms in the periphery. Rather than simply labeling the huge number of atoms as being either symmetric or asymmetric, this investigation aims at exploring a quantitative graph theoretical descriptor of atomic asymmetry. Based on the particular characteristics of the molecules in2D plane, we suggested the weighted atomic sum as the descriptor of atomic asymmetry. Tested by the enumerated atoms in the dataset, the results indicate that the weighted atomic sums are better than the previously reported descriptors.Based on weighted atomic sums, a weighted F index is introduced to represent quantitative molecular chirality in2D, and was validated with all enumerated benzenoids. The results indicate that the weighted F indexes were in accordance with their chiral classification (achiral or chiral) over the whole benzenoids dataset. Furthermore, weighted F indexes were superior to previously available descriptors. Benzenoids possess varieties of shapes and can be extended to approximately represent any shape in2D space-our proposed descriptor has thus the potential to be a general method to represent2D molecular chirality based on the difference between clockwise and anticlockwise surrounding a molecule.(2) Study on Computer-Assisted Structural ElucidationThe CASE system is generated based on a deterministic structure generator which is a slightly modified version of the structure generator in ESESOC system (developed by Prof. Lu Xu in Changchun Institute of Applied Chemistry, Chinese Academy of Science) by introducing the idea of SMOG (developed by Molchanova), and GENM (developed by Molodtsov). It has been tested and proved to be good exhaustiveness and effectiveness. The system is written in Java.So far, the whole frame of CASE system has been basically constructed, and the structure of unknown compound can be elucidated by the NMR data and formula, but it is still far from practical use. The process of structure elucidation is:1) Starting from the formula of the unknown chemicals, all the isomers are produced by the structure generator;2) the candidate structures are screened from all the isomers by NMR data;3) the chemical shifts of candidate structures are predicted by QSPR;4) the candidate structures are ranked on the basis of the similarity between the predicted value and experimental value, and the higher similarity score a candidate structure possesses, the higher possibility the candidate is correct structure.