【作者】 陈伟；

【导师】 孙昊；

【作者基本信息】 东北师范大学 ， 物理化学， 2016， 硕士

【摘要】 众所周知,多重氢键阵列在超分子化学领域应用广泛,并且近年来,大量的化学家致力于研究稳定性强和聚合度高的多氢键阵列超分子聚合物。Leigh课题组第一次在实验上合成出AAAA和DDDD型氢键单体(D:氢键受体;A:氢键受体),在不同环境中皆可以生成结合常数较大的多氢键阵列二聚体,并将这一系列结构成功的应用于超分子化学领域。为了进一步研究对氢键本质及其强度的影响因素,我们通过使用DFT方法研究了相应聚合物的电子结构及其稳定性,并定量计算了二级静电作用、氢键数目、X-H…Y氢键中X原子的电负性及数目、溶剂极性等因素对氢键单体聚合过程的影响。具体工作内容如下：1.我们对基于含有氢键给体N-H和受体N原子的氢键结合单元形成的多重氢键阵列进行理论研究。应用密度泛函理论讨论了二级静电作用、氢键数目、溶剂极性对聚合物稳定性的影响。结果显示,向氢键给体阵列两端引入两个N-H键,使分子间相邻氢键阵列间的二级静电吸引力增强,聚合物的结合能提高了6.28kcal/mol,聚合自由能降低了7.07 kcal/mol;向受体阵列两端引入两个N原子,同样使二级静电吸引力增加,导致形成二聚体的稳定性增强。频率和NBO分析表明,分子间氢键数目增多,X-H…Y氢键表现出明显的红移。能量计算结果表明,二聚体结构中增加两个分子间氢键,使结合能提高了19.78 kcal/mol,自由能降低了12.17 kcal/mol。氢键单体和二聚体的紫外吸收光谱对比研究表明,氢键单体的聚合过程使相应二聚体的吸收峰的个数和对应的最大吸收波长发生改变,该结果对实验上鉴别聚合物是否形成具有很好的指导作用。因此,增加氢键数目是增强氢键阵列稳定性的最有效手段,而增加二级静电作用也能在一定程度上对二聚体的稳定性进行调整,这一结果可以为实验室设计、合成具有特定强度的氢键型聚合物提供有价值的理论指导。2.对三种不同的DDDD型氢键给体与同一AAAA型氢键受体形成的三种二聚体进行DFT模拟。能量计算和AIM分析结果证明,乙腈中,外侧的两个C-H…N键替换成N-H…N,聚合物结合能提高11.29 kcal/mol,聚合自由能降低10.00 kcal/mol;内侧两个C-H…N的影响稍小,结合能提高10.35 kcal/mol,聚合自由能降低7.34 kcal/mol|,即二聚体的稳定性大小顺序为2b>2e>2f。因此,X-H…Y氢键中X原子的电负性是增强氢键型二聚体稳定性的有效手段。结果还表明,溶剂极性对聚合过程也有很大影响,溶剂极性越强,越不利于单体的聚合过程。频率和NBO分析结果显示,我们讨论的所有单体和二聚体中都存在明显的分子内和分子间氢键。核磁共振氢谱和紫外可见吸收光谱的计算结果进一步说明,氢键单体和二聚体结构的光谱性质有很大区别,这为未来鉴别聚合物的形成提供了有力的证据。更多还原

【Abstract】 As we all know multiple hydrogen-bonds arrays have been widely used in supramolecular chemistry, and a larger number of chemists are devoted to the study of polymers based on hydrogen-bonding with strong stability and high polymerization degree in recent years. The efforts of Leigh group in experiment certify that AAAA and DDDD monomers (A:hydrogen-bonding acceptor; D:hydrogen-bonding donor) can form strongly stable dimers in any conditions. To further understand the nature of H-bonds and the influencing factors of polymerization, we accurately calculate the contribution of electronegativity of X atom in X-H…Y, hydrogen bonds number and solvent polarity to the stability of dimers by using DFT method. Detailed results are as follows:Our theoretical calculation of dimer unit is based on hydrogen-bonding donor with N-H and hydrogen-bonding acceptor with N atom. We have performed detailed DFT study about the effect of secondary electrostatic interaction, hydrogen-bonding number and the solvent polarity on the stability of dimers. Adding two N-H bonds in hydrogen-bonds donor unit can improve the binding energy by 5.98 kcal/mol and reduce free energy of dimerization by 7.07 kcal/mol. The Frequency and NBO results of dimers 1a,2b,3d certify that all intermolecular H-bonds show a clearly red shift when monomers form dimers. The calculations of energies indicate that adding two intermolecular hydrogen bonds to dimers will increase the binding energy of 19.78 kcal/mol and will decrease the free energy of 12.17 kcal/mol. Meanwhile, the obvious difference of λmax and absorption peaks number are found between monomers and dimers from UV-visible spectra, and it is can be regarded as a significant evidence to identify the formation of dimers and dimerization degree.DFT simulation is carried out on three dimers formed an AAAA accepter and three DDDD donors. The purpose of this study is to reveal contribution of X atom in X-H--Y to the stability of hydrogen-bond arrays. Energy calculation and AIM analysis indicate that the dimers stabilities have a great decrease when the intermolecular N-H bonds are replaced by C-H bonds in any conditions (vacuum, dichlomathane, acetonitrile, water), respectively, the binding energy of N-H…N is about 5.41 kcal/mol larger than C-H…N, and the dimers stabilities in order of 2b> 2e> 2f. Meanwhile, the polarity of sovent has a clear influence on the polymerization process. Geometries and NBO analyses prove that intramolecular and intermolecular hydrogen bonds exist within the monomers and dimers.1H NMR and UV-visible spectra show an evident difference of between monomer and dimer, it may be used a powerful information to distinguish the formation of polymers.更多还原