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瓜环是超分子化学中的重要一支。在气相环境中,使用密度泛函理论(DFT)优化了由n个苷脲单元组成的瓜环[n](CB[n](n=5~10)),并使用密度泛函(DFT)概念指数和Multiwfn软件包等现代量子化学工具,计算和分析了CB[n](n=5~10)的结构参数、前线轨道能量值和化学稳定性。结果表明:α-N结构最稳定,α=O、γ-γ、γ-H和β-H(2)结构的化学稳定性较差;部分键角的变化以CB[6]为界,主要二面角的变化呈现中心对称的形式;随着苷脲单元n的增加,CB[n](n=5~10)的端口直径(c)、空腔直径(b)和圆外径(a)线性增大;前线轨道E_(HOMO)、E_(LUMO)值及E_(LUMO)-E_(HOMO)值逐渐降低,化学活性逐渐增强、稳定性逐渐减弱;端口O原子是最大的亲电活性位点,LUMO的电子云分布主要与H原子有关,且次甲基H原子对LUMO电子云的贡献最大;次甲基C原子、亚甲基C原子和指向CB[n]端口方向的亚甲基H原子对LUMO的电子云分布具有抑制作用,抑制能力的大小为指向CB[n]端口方向的亚甲基H原子>亚甲基C原子>次甲基C原子。这可为研究瓜环的超分子组装提供理论依据。
Melon ring is an important supramolecular chemistry. In gas phase, guanidine [n] (CB [n] (n = 5-10)) consisting of n glycoside units was optimized using density functional theory (DFT) and density functional theory Concept index and Multiwfn software packages, the structural parameters, frontier orbital energy values and chemical stability of CB [n] (n = 5 ~ 10) were calculated and analyzed. The results show that the α-N structure is the most stable and the chemical stability of α = O, γ-γ, γ-H and β-H (2) The dihedral angle changes in a centrosymmetric form. With the increase of glycosidic unit n, the port diameter (c), the cavity diameter (b) and the circular outer diameter (a) of CB [n] ) Linearly increased. The values of HOMO, EUMO and EUMO of the frontier orbit decreased gradually, and the chemical activity gradually increased and their stability decreased gradually. The O atom of the port was the largest electrophilic activity Sites, the distribution of LUMO electron cloud is mainly related to the H atom, and the contribution of the H atom to the LUMO electron cloud is the largest. The methionine C atom, the methylene C atom and the methylene to the CB [n] The base H atom has an inhibitory effect on the LUMO electron cloud distribution, and the inhibitory capacity is the size of the methylene H atom> the methylene C atom> the methine C atom in the direction of the CB [n] port. This may provide a theoretical basis for the study of supramolecular assembly of guanidine ring.