直接键连C-X(X=H, C)的核自旋偶合常数的理论研究

利用建立的PM3级别上的最大重迭对称性分子轨道法和自然杂化轨道方法，计算了系列烃类化合物的杂化轨道和电荷分布，拟合出计算C-H及C-C偶合常数的简单关系式，研究了各种烃类分子中不同的C-Ｈ键和Ｃ-Ｃ键偶合常数，理论计算值和实验数据都较为吻合. 进一步验证了直接键连1JCX(X=C, H)偶合常数主要取决于偶合作用中的Fermi接触相，为从简单价键理论角度解释和计算1JCH和1JCC提供了一种简便直观的方法. 计算结果也表明提出的计算方法是可行的.

Theoretical study on spin - spin coupling constants of C-X (X= H, C) bonds

By using of the density matrix and the net atomic charges obtained from calculation procedure of the maximum overlap symmetry molecular orbital (MOSMO) method under PM3 approximation presented in previous paper, the natural hybridized orbital (NHO) procedure has been performed. Further, the correlativity between the NHO calculation results and the nuclear spin-spin coupling constants of the directly bonded C-H and C-C bonds has been obtained. The calculated values are all in good agreement with the experimental data, which supports the Fermi contact term is a dominant factor in determining carbon-Hydrogen and carbon-carbon spin-spin constants. Thus one is able to interpret and calculate the 1JCH and 1JCC values based on the simple valence bond theory. Thus, it further illustrate that MOSMO method under PM3 approximation is reasonable.