Theory Study On Molecule Configuration And Character Of Oxalic Acid And Oxalyl Halides

Oxalic acid is the simplest dualistic acid, its exceptional configuration and particular chemistry character is attended all along. Chemists widely study oxalic acid and oxalyl halides by spectrum detection, crystal structure analysis and theory calculation and so on. In this paper, high-level quantum chemistry calculation methods are used to theoretically investigate basic configuration, conformers, torsion potential energy surface and internal rotation transition state of oxalic acid and oxalyl halides. Oxalyl bromide as the typical system is studied on its dissociation channel.The whole paper consists of seven chapters. Chapter 1 mainly reviews the evolution of oxalic acid and oxalyl halides. The second chapter summarizes the theory of quantum chemistry and calculation methods of this paper.In the third chapter, the optimization and frequency analysis of thirteen possible structures of oxalic acid have been calculated, by using ab initio MP2, density functional method (B3LYP) and SCF-HF with 6-311++G** basis set. The results show that oxalic acid has eight local minima and five transition states of internal rotation configurations. Accordingly, The most stable isomer I has been analyzed with MO and NBO by using MP2/6-311++G** method. The effect of C-C bond on stability of oxalic acid is discussed, and the relationship between forms and characteristics of oxalic acid is also reported.In the fourth chapter, the configuration of oxalyl fluoride neutral molecule (FCO)2 is studied at HF MP2 QCISD and B3LYP level with 6-311++G** basis sets. The result that (FCO)2 have trans and gauche conformers are consist with spectrum analysis. At B3LYP/6-311++G** level, the stability of two conformers are studied by MO and NBO analysis. Furthermore, the vibrational mode is obtained by frequency analysis and IR spectrum chart is simulated, which is consisting with experiment result.In the fifth chapter, the conformers of oxalyl bromide cation (BrCO)+2 is studied at the BHandHLYP level with 6-311+G(d) and 6-311+G(2df) basis sets. It is found that (BrCO)+2 have trans and gauche conformers. Hyperconjugation exist in gauche form. Furthermore, the study of the dissociation reaction Gibbs free energy of oxalyl bromide cation (BrCO)+2 and neutral molecule (BrCO)2 show that the dissociation of C-C bond in (BrCO)+2 is easier...