Theoretical Study On The Spin-spin Coupling Constant Of Indirectly Bonded Atoms

Nuclear magnetic resonance (NMR) is one of modern analytic methods. The structural information of molecular geometric structures and bonds between atoms, the interaction between atoms can be obtained by study on nuclear magnetic resonance. With the development of technology, NMR is widely used in all kinds of fields. At the present, NMR is a valuable tool in the research of geometric structures, physical properties, dynamic states of molecules. At the same time, it is also used in organic chemistry, biology chemistry, macromolecule chemistry, inorganic chemistry, environmental chemistry and life science. Therefore, the research of NMR is beneficial to study the material world deeply for chemists.The chemical shift and the spin-spin coupling constant are two important parameters of NMR. By now, experimental values of chemical shifts have been every accurate. But the values of spin-spin coupling constants have not been researched deeply. Along with the development of quantum chemistry, the calculation of the spin-spin coupling constant has become a concerned problem of quantum chemistry in recent years. According to the spin-spin coupling constant and the splitting ofpeaks, we can designate the spectra lines, estimate the position of the substitutes, to which the spectra lines belong.Theoretical study on spin-spin coupling constants of directly bonded atoms has been reported in the relative references. On the contrary, the study on spin-spin coupling constants of indirectly bonded atoms has never been widely discussed. Therefore, it is interesting to use reliable and accurate methods of quantum chemistry to calculate the spin-spin coupling constants of indirectly bonded atoms.According to the equations in the relative references. A series of theoretical calculations on spin-spin coupling constants of indirectly bonded atoms have been done in this paper.Firstly, a series of formulas of different kinds of atoms have been deduced according to the equation in the relative references. Then twenty-two compounds that have F-C-H bonds in their molecular formulas have been studied by the method of B3LYP/6-311G, B3LYP/6-311++G, MP2/6-311G, MP2/6-311++G. Four equations have been obtained. Relative parameters of some compounds have been introduced to these equations . The results show that the best program for calculating the spin-spin coupling constant is B3LYP/6-311G.Then, spin-spin coupling constants of indirectly bonded atoms such as C-H, C-F, C-C have been calculated at the B3LYP/6-311G level. Relative equations have been obtained. In addition, relative parameters of some compounds have been introduced to these equations, the results are basically consistent with the experimental values.In addition, the spin-spin coupling constants of indirectly bonded atoms such as H-H have been studied, the results of calculations are not consistent with experimental values very well. The reason is that the spin-spin coupling constant of the kinds of atom is small and the accuracy of the equation is not enough.The above-mentioned calculated results show that, the method we have discussed in the article can be used to calculate the spin-spin coupling constants of indirectly bonded atoms whose experimental values is small.