【作者】 郭勇；

【导师】 谢代前；

【作者基本信息】 四川大学 ， 物理化学， 2003， 博士

【摘要】 分子振动光谱的理论研究，对于解释和预测振动光谱的实验结果，了解分子的能级、结构、电子组态、化学键的性质等多方面物质结构的知识有着重要的意义。本文采取量子化学的密度泛函理论B3LYP和较大的基组，从计算分子的理论平衡构型及其谐性二阶力常数着手，对于实验难于进行光谱数据的测定，或者测定后在基频的确定和振动模式的指认中还存在疑问的6个有机生物大分子，2—氟—5—溴吡啶、尿素、尿酸、士的宁、硝酸士的宁、依卡精的振动光谱进行了比较系统的研究，主要结论如下： 1．用密度泛函理论方法B3LYP以及6-311++G(2df，2pd)基组对2-氟-5-溴吡啶分子的平衡几何构型进行了优化，在此基础上计算了该分子的振动谐力场。根据实验已有的观测值，按照振动模式的分类使用了一套对于力常数的校正因子，使用Pulay的标度方法对理论力场进行了标度。采用Wilson的GF矩阵方法，根据标度后的理论力场进行了简正坐标分析，对2-氟-5-溴吡啶分子的振动基频进行了理论研究，四川人学博十学位论文得到了势能分布和红外振动频率.与红外频率的实验值相比较，理论频率的平均偏差为14 cm一‘.此外，根据振动模式的势能分布对此分子的振动基频进行了合理的理论归属和解释， 2.采取BLYP/6一3 11++G(Zdf，Zpd)及B3LYP/6一311++G(Zdf，Zpd)对尿素和尿酸的振动光谱进行研究，从理论上在确定了分子的平衡几何结构，在此基础上得到了尿素、尿酸分子的笛卡尔坐标下的力常数，根据其空间对称性定义了对称内坐标，完成了力常数在笛卡尔坐标到对称坐标的转化。利用GF矩阵方法和SQM标度力常数方法，根据已有的实验数据，主要根据不同的振动模式提出了相应的一套力常数标度因子，计算得到了研究分子的振动频率及其相应的红外强度.尿素，尿酸分子经过校正后的频率相对于实验频率的平均偏差分别为17cm一‘和27cm一’。根据优化的SQM力场，采用一套非多余的内坐标体系，我们计算了尿素和尿酸分子的简正振动频率的势能分布.根据PED分布，对于文献中没有或者归属不明的尿素、尿素分子的各个红外振动给出了明确和完善合理的指认，并进行了相应解释。利用得到的SQM力场，预测了尿素的D取代同位素分子的振动频率，理论计算的结果同实验观测值取得了相当的一致。同时根据理论计算的振动光谱，还对尿素、尿酸的振动光谱进行了比较，发现两个分子的CO伸缩以及面外弯曲振动等特征基团的振动频率比较一致。3.采用从头算B3LYP/6一31G*的理论方法，对马钱子中的生物碱四川大学博士学位论文士的宁、依卡精以及硝酸马钱子的构型进行了优化，得到了优化的平衡构型，并对其结构进行了比较，从理论上对于这三种多环结构的复杂天然分子的构型差异给与了解释。在平衡优化构型的基础上计算了他们的振动谐力常数、红外光谱频率以及强度。根据士的宁分子的实验红外光谱数据，按照Pulay等提出的校正方法，根据对于红外光谱的理论计算的指认结果，对于不同类型的振动模式的频率采用相应的校正因子对频率进行了校正，理论计算与实验频率之间的平均误差为19 cm一‘。说明这种校正方法对于研究多环的大分子的红外光谱是可行的。在对士的宁分子红外光谱理论研究的基础上，将所得到的一套标度因子用于目前还未见报道的依卡精、硝酸士的宁的红外光谱预测之中，并结合理论计算的强度对依卡精、硝酸士的宁的红外光谱进行了振动模式的指认。对于士的宁、硝酸士的宁、易卡精分子的相关特征振动进行了解释和预测，并对三者的红外光谱的研究结果进行了比较。更多还原

【Abstract】 The theoretical studies of geometries and vibrational spectra for complex organic molecules can provide significant information about understanding and predicting the infrared spectra, molecular structures, electronics configurations, and chemical bonds.Usually, a complete infrared spectrum is difficult to determine and assign by experimental methods. Quantum chemistry theoretical study can optimize the geometries, calculate the vibrational force fields ,vibrational frequencies and infrared intensities of the target molecule. In this paper, we used the density function theories method B3LYP and large basis sets to calculate and assign the vibrational spectra of important molecules 2-fluoro-5-bromopyridine, urea, uric acid, strychnine, strychnine nitrate and icajine, and the following conclusions are drawn out:1. The optimized geometries, harmonic force fields and infrared spectra of the 2-fluoro-5-bromopyridine molecule were calculated by density functional theory B3LYP method with 6-311++G(2df,2pd) basis set. The theoretical force field was scaled using the scaled quantum mechanical scheme. The error of frequencies was found to be 14 cm-1. The assignment of the vibrational fundamentals for the 2-fluoro-5-bromopyridine molecule was also performed according to the potential energy distributions.2.On the other hand, the optimized geometries, harmonic force fields, infrared frequencies and intensities of the urea and uric acid moleculewere calculated by density functional theory BLYP and B3LYP respectively with 6-311++G(2df,2pd) basis set. The theoretical force field was scaled using the scaled quantum mechanical scheme with a set of scaling factors. The error of frequencies was found to be 17 cm-1 for urea and 27 cm-1 for uric acid. The assignment of the fundamentals for urea and its deuterated isotopemer CO(ND2)2 were performed according to the potential energy distributions, and the same were done for uric acid .3. In addition, density functional theory B3LYP calculations using 6-31G* basis set were carried out to study the molecular structure, force fields, vibration spectra of the strychnine, strychnine nitrate, icajine molecules. The optimized geometries, harmonic force fields, vibrational frequencies, IR intensities have been obtained. A set of scaling factor for calculated frequencies was constituted for strychnine and translated to strychnine nitrate arid icajine to predict their vibrational spectra. Normal mode analysis were performed to assign the vibration fundamental frequencies for strychnine, strychnine nitrate and icajine. According to the assignments,we predict and compare the vibrational spectra of strychnine, strychnine nitrate and icajine. The error of frequencies was found to be 19 cm-1 for strychnine.The computational freaquencies are in good agreement with the observed results.更多还原