改进的Hückel分子轨道方法(Ⅻ)——芳烃基多烯醛电子光谱的研究

The Modified Huckel Molecular Orbital Method(Ⅻ) Studies on Electronic Spectra of Phnylpolene Aldehydes

本文针对芳烃基多烯醛(C_6H_5-(CH=CH)_n-CHO)提出了两种改进的Huckel分子轨道方法的方案:MHMO(Ⅰ)与MHMO(Ⅱ)。在MHMO(Ⅰ)中,假定直链与苯环中的C=C键的键积分为β,苯环中C-C键的键积分为β,直链中C-C键的键积分为β′=ηβ,C=O键的键积分为β″=1.5β。氧原子的库伦积分参数为h_0=1。其他Huckel假定不变。对η=β′/β提出了3个计算公式。在MHMO(Ⅱ)中,直链中的C-C键的键积分为β=0.65β,其他与MHMO(Ⅰ)假定一样。利用两种MHMO方法,对芳烃基多烯醛进行了计算,得到了它们的π—电子能级,分子轨道系数等。预示了芳烃基多烯醛的最大吸收波长或波数,与实验值符合较好。比HMO方法有非常明显的改进。

This paper has reported two modified Huckel molecular orbital me- thods,which are directed against spectra of phenylpolyene aldehydes. In the first method (MHMO (I)). the bond integral of C=C double bonds is assumed equal toβ.the bond integral of C--C single bonds (ring) β; the bond integral of C--C single bonds (chain) β′=ηβ; the bond integral of C=O bondsβ″′=1,5β, The parameter value of coulomb integral for oxygen atom is h_0=1. The rest of Huckel assumptions were retained. Three different calculation formulas were put forη=β′/β In the second me- thod (MHMO (Ⅱ)), the bond integral of C--C single bonds β′=0.65β. The rest of MHMO (Ⅰ) assumption were retained. With these two me- thods, MHMO calculations on phenylpolyene aldehydes for n=1-17 were carried out,Pi-electron energies,MHMO confficient. and the like have been obtained.Comparison of predicted and observed longest-wave lenth absorption (or wave numbers)for phenylpolyene aldehydes shows fair agreement with experiment. There is much improvement compared with HMO.