3-氨基-2,5-二氯苯甲酸振动光谱的密度泛函研究

为了本质地把握3-氨基-2,5-二氯苯甲酸(3A2,5DBA)的振动光谱和结构间的关系,在HF和B3LYP水平上利用6-311G(d,p)基组对3A2,5DBA进行了结构优化和振动频率的计算,得到了3A2,5DBA的结构信息和全部45个简正振动模式.通过与苯甲酸的结构参数以及相关文献数据的对比,发现B3LYP/6-311G(d,p)方法较HF/6-311G(d,p)方法能给出更加合理的结果.考虑到计算模拟分子和实验测量样品间的差异,对计算所得到的频率进行了合理的标度修正.在B3LYP/6-311G(d,p)方法下,对波数小于800cm-1的振动频率,标度因子取1.001 3,而波数大于800 cm-1的标度因子取0.961 3.借助Gaussian View程序包对所计算得到的振动模式进行了高精度指认,对3A2,5DBA的主要官能团及取代基团进行了振动分析.通过和实验测量的FTIR数据的比对,发现经标度修正后的计算结果和实验测量符合的很好.同时结合相关的文献报道,表明所做的振动指认和振动分析是合理的.

The study of vibrational spectra of 3-amino-2, 5-dichlorobenzoic acid by density functional theory

To understand the relationship between the vibrational spectra and the geometry structure of 3-amino-2, 5-dichlorobenzoic acid (3A2, 5DBA) essentially, geometry optimizations and vibrational frequencies calculation of 3A2, 5DBA were performed at Hartree-Fock (HF) and Becke's three-parameter hybrid functional (B3) for the exchange part and the Lee-Yang-Parr (LYP) correlation function (B3LYP) level using 6-311G(d, p) basis set, respectively. The structural information and 45-complete normal vibrational modes of 3A2, 5DBA were obtained. Comparing the computational geometric parameters of 3A2, 5DBA with the values observed in experimental measurement of benzoic acid as well as the computed vibrational frequencies of 3A2, 5DBA with the reported data of pertinent literature, it was revealed that the results coming from B3LYP/6-311G(d, p) are more reasonable than those by HF/6-311G(d, p). Taking into account the difference between the computed 3A2, 5DBA molecule and the experimental measured sample, the calculated vibrational frequencies were reasonably scaled. Under the B3LYP/6-311G(d, p) method, the scale factor was 1.0013 for the vibrational frequencies with wave numbers <800 cm(-1), while the scale factor was 0.9613 for the vibrational frequencies with wave numbers >800 cm(-1). With the help of Gaussian View software package, the theoretically calculated vibrational frequencies were assigned much more accurately. In addition, the vibrational analysis of substitutive groups and main functional groups of 3A2, 5DBA was carried out. Through the comparison of the calculated vibrational frequencies with the frequencies of 3A2, 5DBA observed in FTIR experiment, the authors found that the theoretically calculated vibrational frequencies scaled reasonably were in excellent agreement with the data coming from experimental measurements. Meanwhile, according to the related literature reports, it was shown that our work done in the paper about vibrational assignments and vibrational analysis of 3A2, 5DBA turned out to be reasonable.