【作者】 陈晓；

【导师】 步宇翔；

【作者基本信息】 山东大学 ， 物理化学， 2023， 硕士

【摘要】 小尺寸的环状和笼状烷烃及多面体烷烃,它们好的分子对称性、独特的物理化学性质引起化学界很大的兴趣和重视。全氟化能够对烷烃产生深远影响,小尺寸的环状和笼状全氟烷烃及多面体碳氟化合物都表现出较强的结合电子能力。一个过剩电子与碳氟化合物相结合形成稳定的溶剂化电子体系。不同于传统的电子体系中强束缚电子（如键合电子或孤对电子）,溶剂化电子体系中溶剂化电子是具有明显弥散性和里德堡特征的弱束缚电子。目前为止,尽管已经有许多关于溶剂化电子体系结构、性质和应用的研究方面的报道,但是,碳氟化合物俘获的溶剂化电子特征及溶剂化电子如何调控核自旋-自旋耦合性质等方面的研究还较少。本论文主要利用密度泛函理论、电子定域化函数分析和自然键轨道分析探究碳氟化合物溶剂化电子体系中溶剂化电子状态、分布和性质,揭示溶剂化电子调控碳氟化合物中核自旋-自旋耦合的机制及规律。主要的结论及创新点如下:（1）小尺寸的环状和笼状全氟烷烃中通过溶剂化电子间接核自旋-自旋交换耦合:小尺寸的环状和笼状全氟烷烃(c-C_nF_2n（n=3,4,5）,C_nF_n（n=4,6,8）)可以俘获一个过剩电子形成溶剂化电子体系。研究发现,溶剂化电子在C-C键（成键特征分布）和C-F键（反键特征分布）上特殊分布使小尺寸的环状和笼状全氟烷烃表现出C-C键缩短,C-F键伸长的总体变化。此外,溶剂化电子作为一种强的介入电子,它可以异常地增强NeJFF。重要的是,具有特殊分布、状态和性质的溶剂化电子触发了一种不同于传统“通过-键（T-B）”和“通过-空间（T-S）”耦合传输机制的新型基于溶剂化电子（esol-based）耦合传输机制,它包括两条耦合路径:“通过-溶剂化电子（T-SE）”耦合路径和“溶剂化电子增强的T-B和T-S（esol--enhanced T-B⊕T-S）”耦合路径。T-SE耦合影响因素是耦合路径的角度,而esol--enhanced T-B⊕T-S耦合影响因素是耦合路径的距离。随着最短T-B耦合路径上化学键数目增加,T-SE耦合逐渐占据主导地位。两条耦合路径通过竞争和合作关系,共同实现和调控大的NeJFF。本工作不仅丰富了对弱束缚电子体系中耦合机制的理解,也为大气扩散研究中F-核磁共振探针的设计和基于溶剂化电子的电子器件的设计提供了有用的信息。（2）全氟[n]棱烷和全氟[n]星烷中通过溶剂化电子不同寻常的J-耦合:全氟[n]棱烷（棱柱形（C₂F₂）_n（n=3-8））和全氟[n]星烷（星形（C₃F₄）_n（n=3-5））表现出强烈的全氟笼效应,即它们可以将过剩电子稳定地封装在笼内,进而可以俘获一个过剩电子形成多面体碳氟溶剂化电子体系。研究发现,溶剂化电子在棱柱形e@（C₂F₂）_n（n=3-8）和星形e@（C₃F₄）_n（n=3-5）基态轨道是类-2s（2s-like）型特征分布,这主要源于化合物特殊的多面体结构,它允许溶剂化电子滲透到C-壳层和C-F键区域,从而扩展和修改了溶剂化电子轨道尾部。2s-like型分布的溶剂化电子触发了一种新型基于溶剂化电子耦合机制,它包括两条耦合路径:“通过-溶剂化电子（T-SE）”耦合路径和“溶剂化电子增强的T-B和T-S（esol--enhanced T-B⊕T-S）”耦合路径。有意义的是,当两个耦合F核与多面体中心之间夹角（∠F?F）<70°时,最短T-B耦合路径上化学键数目（N）是3或4,并且两个耦合F核之间空间直线距离(d_FF)较短,esol--enhanced T-B⊕T-S耦合对^N（e）J_FF的贡献（JTB+TS）决定^N（e）J_FF的符号、绝对值大小和变化特征。此时,^N（e）J_FF是负值且^N（e）J_FF的绝对值随着∠F?F和d_FF增加而减小。当∠F?F>70°时,N是4或大于4,并且d_FF较长,T-SE耦合对^N（e）J_FF的贡献（JT-SE）决定^N（e）J_FF的符号、绝对值大小和变化特征。此时,^N（e）J_FF是正值且^N（e）J_FF的绝对值随着∠F?F和d_FF增加而增大。这项工作不仅进一步丰富了关于溶剂化电子状态、分布和性质的信息,还提供了关于多面体碳氟化合物中溶剂化电子触发或改进的原子核自旋性质的见解。综上所述,本论文主要利用密度泛函理论、电子定域化函数分析和自然键轨道分析对小尺寸的环状和笼状全氟烷烃、全氟[n]棱烷和全氟[n]星烷结合一个过剩电子形成的溶剂化电子体系分子结构、电子性质和电子效应进行了系统的研究,并揭示了溶剂化电子调控间接氟核自旋-自旋耦合的机制及规律,为溶剂化电子体系在核磁共振探针实际领域的应用提供了理论依据。更多还原

【Abstract】 Small sizes of cyclic and cage-shaped alkanes,as well as polyhedral alkanes,have attracted great interest and attention in the chemical community due to their good molecular symmetry and unique physical and chemical properties.Perfluorination can have a profound impact on these alkanes,and small sizes of cyclic and cage-shaped perfluoroalkanes,as well as polyhedral fluorocarbons,exhibit the strong ability to bind an additional electron.An additional electron combines with these fluorocarbons to form stable solvated electron systems.Unlike strongly bound electrons（i.e.bonding electrons or lone pair electrons）in traditional strongly electron systems,solvated electrons in solvated electron systems are weakly bound electrons with distinct dispersion and Rydberg characters.Up to now,there have been many studies on the structures,properties and applicatons of solvated electron systems,however,there are few studies on the characters of solvated electrons captured by fluorocarbons and how solvated electrons regulate the nuclear spin-spin coupling properties.This paper mainly explores the states,distributions and properties of solvated electrons in fluorocarbon solvated electron systems through density functional theory,electron localization function analysis,and natural bond orbital analysis,and reveals the mechanisms and rules of solvated electrons regulating the nuclear spin-spin coupling of fluorocarbons.The main conclusions and innovations are as follows:（1）Indirect Nuclear Spin-Spin Exchange Coupling through Solvated Electron in Small Sizes of Cyclic and Cage-Shaped Perfluoroalkanes:Small sizes of cyclic perfluoroalkanes(c-C_nF_2n（n=3,4,5）)and cage-shaped perfluoroalkanes（C_nF_n（n=4,6,8））can capture an additional electron to form solvated electron systems.Reasearch has found that the special distributions of solvated electrons on C-C bond（bonding character distribution）and C-F bond（antibonding character distribution）results in the general change in the C-C bond shortening and C-F bond elongating of small sizes of perfluorocycloalkanes and cage-shaped perfluoroalkanes.In addition,as strong intervening electrons,solvated electrons can abnormally enhance NeJFF.Improtantly,solvated electrons with special distributions,states and properties trigger a novel coupling transmission mechanism based on solvated electron（esolbased）,which is different from traditional "through-bonds（T-B）" and "through-space（T-S）"coupling transmission mechanisms,including two coupling paths:"through-solvated electron（T-SE）" coupling path and "solvated electron enhanced T-B and T-S（esol--enhanced T-B⊕T-S）"coupling path.The influencing factor of T-SE coupling is the angle of coupling path,while the influencing factor of esol--enhanced T-B⊕T-S coupling is the distance of coupling path.With the increase of the number of chemical bonds on the shortest T-B coupling path,T-SE coupling gradually dominates.The two coupling paths jointly realize and regulate the large NeJFF through competition and cooperation.This work not only enriches the understanding of the coupling mechanism in weakly bound electron systems,but also provides useful information for the design of F-NMR probes in atmospheric diffusion research and the design of esol--based electronic devices.（2）Unusual J-Couplings through Solvated Electron in Perfluoro-[n]Prismanes and[n]Asteranes:Perfluoro-[n]prismanes（（C₂F₂）_n,n=3-8）and[n]asteranes（（C₃F₄）_n,n=3-5）exhibit a strong perfluoro cage effect,that is,they can stably encapsulate an additional electron within the cage,and then capture an additional electron to form polyhedral fluorocarbon solvated electron systems.Reasearch has found that the ground-state orbitals of solvated electrons exhibit a 2s-like type characteristic distribution in prism-shaped e@（C₂F₂）_n（n=3-8）and aster-shaped e@（C₃F₄）_n（n=3-5）,mainly due to unique polyhedral structure that allows solvated electrons to penetrate the C-shell and C-F bond regions,extending and modifying the tail of solvated electron orbitals.The 2s-like type distribution of solvated electrons triggers a novel coupling mechanism based on solvated electron（esol--based）,including two coupling paths:"through-solvated electron（T-SE）" coupling path and "solvated electron enhanced T-B and TS（esol--enhanced T-B⊕T-S）" coupling path.Significantly,when the angle（∠F?F）between two coupled F nuclei and the polyhedral center is smaller than 70°,the number（N）of chemical bonds in the shortest T-B coupling path is 3 or 4,and the spatial linear distance(d_FF)between two coupled F nuclei is short.And the contribution（JTB+TS）of esol--enhanced T-B⊕T-S coupling determines the sign,absolute value and change character of ^N（e）J_FF.In this case,the sign of ^N（e）J_FF is negative and |^N（e）J_FF| decreases with the increase of ∠F?F and d_FF.When ∠F?F is larger than 70°,N is 4 or>4 and d_FF is long,the contribution（JT-SE）of T-SE coupling determines the sign,absolute value and change character of ^N（e）J_FF.In this case,the sign of ^N（e）J_FF is positive and |^N（e）J_FF| increases with the increase of ∠F?F and d_FF.This work further not only enriches the information about the states,distributions and properties of solvated electrons,but also provides insights into the nuclei spin properties triggered or improved by solvated electrons in fluorocarbon compounds.In summary,in this paper,density functional theory,electron localization function analysis and natural bond orbital analysis were utilized to systematically explore the molecular structures,electronic properties and electronic effect of small sizes of cyclic and cage-shaped perfluoroalkanes,as well as perfluoro-[n]prismanes and perfluoro-[n]asteranes solvated electron systems.This paper revealed the mechanisms and rules of solvated electrons regulating indirect fluorine nuclear spin-spin coupling,providing theoretical bases for the application of solvated electron systems in the practical field of nuclear magnetic resonance probes.更多还原