取代基对2-(4-取代苯基)-5-取代嘧啶紫外吸收能量的影响

The Influence of Substituents on the UV Absorption Energies of 2-(4-X Phenyl)-5-Y Pyrimidines

测定了46个2-(4-X苯基)-5-Y嘧啶的紫外可见吸收光谱,研究了共轭链两端取代基X,Y对紫外最大吸收波长λ_(max)对应的能量v_(max)的影响规律,提取表征基态取代基电子效应的Hammett参数σ和表征激发态取代基电子效应的激发态取代基参数σ^(ex)_(CC)对v_(max)建立定量结构-性质相关模型,得到了相关系数高(R^(2)=0.9487)、平均相对误差小(D=1.26%)的5参数模型.结果表明,取代基X,Y的共轭效应、激发态取代基效应及取代基的交叉相互作用对化合物的紫外吸收有较大影响.结合各参数前面的系数对模型的物理意义进行了合理解释,并与本课题组之前研究的取代基对2-X-5-Y嘧啶类化合物的紫外吸收能量的影响规律进行了比较.

The UV-visible absorption spectrums of 462-(4-X phenyl)-5-Y pyrimidines were recorded in anhydrous ethanol.The effects were discussed,that of substituents X and Y at the ends of the conjugate chain on the UV absorption energy v_(max),which corresponding to the maximum absorption wavelengthλ_(max).Hammett parameters(σ,σ_(F),σ_(R))and the excited-state substituent effect parameterσ^(ex)_(CC),characterizing the substituent electronic effects of the ground state and the excited state respectively,were employed to regress against v_(max).A five-descriptor model was built with high correlation coefficient(R^(2)=0.9487)and small average relative deviation(D=1.26%).The results indicate that the conjugate effect descriptor,excited-state substituent effect parameter and the cross interaction parameter of substituents X and Y have great effect on the UV absorption.The physical meaning of the model is elucidated based on the regression coefficients before each descriptor.The substituent effects on the UV absorption of 2-(4-X phenyl)-5-Y pyrimidines are compared to those observed in2-X-5-Y pyrimidines before.