取代基效应对脂肪醇13C NMR化学位移的影响

用原子电负性、静电作用、极化度作为基本参数，并结合表征原子空间连接方式的立体效应参数，对醇分子中不同环境碳原子的化学位移进行关联, 将120个模型化合物(91个脂肪一元醇, 29个二元醇)中747个碳原子相关参数值和化学位移值带入模型中得到如下估算方程:  δ_C=42.947 9 + 63.064 0Q_i-3.628 6F+5.121 3Σα_x-6.584 8Q_iΣα_x -4.842 7N^α_H-0.585 5N^γ_H-4.104 6N^γ_OH (R=0.998 1 R²=0.996 1 S=1.14 F=27 125.2 n=747)  方程中各参数物理意义比较明确. 通过用“留一法”(LOO)检验(R_cv=0.998 0，R²_cv = 0.996 0，S_cv=1.16)及对样本外5个化合物69个碳原子化学位移的预测值和实验值比较, 结果表明模型方程具有很好的稳定性和预测精度, 该模型的提出为以后计算更加复杂化合物的¹³C NMR化学位移奠定了良好的基础.

Influence of Substituent Effects on the 13C NMR Chemical Shifts of Aliphatic Alcohols

An empirical model for calculating ¹³C chemical shifts of aliphatic alcohols was proposed, in which the parameters describing the chemical environment of the focused carbon atoms are in were used as the independent variables. The parameters included electronegativity, atomic polarizability and those representing the steric effects. The experimentally-measured ¹³C NMR chemical shifts of 747 carbon atoms in 120 model compounds (91 alcohols and 29 diols) were used as the training set to derive the weights for the independent variables. The correlation coefficient R of the model was found to be 0.998. Leave-one-out cross-validation demonstrated good predictive ability and stability of the model. The model proposed was used to calculate the ¹³C chemical shifts of 69 different carbon atoms in 5 compounds that were not included in the training set, and the results proven to be satisfactory. The proposed model may be useful for calculating ¹³C NMR chemical shifts in alcohols with complex structures.