| Studies of the intermolecular interactions are very important, because the intermolecular interactions play a key role in clarifying the mechanism of biological reactions and revealing the nature of the phenomenon of life. Intermolecular interaction is a very active subject because of its important role in chemistry, physics, and biology. Intermolecular interactions can produce a variety of non-covalent interactions, the most common mode of which is the electron transfer from the region of electron concentration to the region of electron depletion. In the past two decades, the intermolecular interactions between OCS, CO2, N2O and other small molecules with series hydrocarbon have attracted much attention. Because alkene, alkyne and benzene have the π-cloud electronic structure with abundant negative electrostatic potential, then they can easily interact with various partners as electron donors. In this thesis, the intermolecular interactions on S…π and π…π interactions between Greenhouse gases (OCS, CO2, N2O) and hydrocarbon (C2H4, C2H2, C4H6, CeHe) have been studied by quantum chemistry method and quantum theory of "atoms in molecules"(QTAIM) investigations. Therefore, this work not only could help us to obtain a detailed explaining of the experiments, but also help us to obtain a detaile understanding of environmental science, astronomy and basic sciences.In this work, the intermolecular interactions on S…π and π…π between Greenhouse gases(OCS, CO2, N2O) and hydrocarbon (C2H4, C2H2, C4H6, C6H6) have been studied by MP2method and quantum theory of "atoms in molecules"(QTAIM) investigations. In this work, the optimized geometrical parameters computed at a variety of methods and basis sets, and the MP2/aug-cc-pVDZ calculated geometrical parameters are more consistent with the experi- mental data than those obtained by the other methods. The configurations of these complexes were obtained with no imaginary frequencies, which indicated that the configurations of these complexes were equilibrium geometries. All calculations are carried out using the Gaussian03program package. A detailed analysis of the electron density distribution function was made according to QTAIM as proposed by Bader, using the programs AIM2000and AIMALL. The contour maps of Laplacian of%electron density and the contour maps of ELF of π electron density were obtained, using the programs AIM2000, TopMod and GTA-2010. The program GTA-2010was developed by the authors and registered at the QCPE (register number QCPE-661). At the same time, in this work, the electrostatic potentials have been computed and the three-dimensional MEP maps were showed. NBO analysed the transfer of the charge. The main contents are the following aspects:1. The T-shaped complexes OCS…hydrocarbon were investigated at the B3LYP/6-311++G(d,p), B3LYP/aug-cc-pVDZ, MP2/6-311++G(d,p), MP2/aug-cc-pVDZ, and MP2/aug-cc-pVTZ levels of theory. The S…π bonding interaction was studied by topological analysis of electron density. The σ and π electron density was separated, the%electron density function was obtained, and the bonding character of this kind of π-type interaction could be described visually and quantificationally. The outcome indicated that the more carbon atoms in the electron donors, the larger the binding energy of the T-shaped complexes, and the more extent of the red shift of S-C and C-O bonds. The nature of interactions of OCS and hydrocarbon are S…π interactions, which belong to noncovalent "closed-shell" electrostatic interactions. The more carbon atoms in the electron donors, the greater the electrostatic interaction is. The topological parameters (ρb,△2ρb,Gb, and Vb) have linear relations with the interaction energies.2. The complexes OCS…C6H6, C6H6…Rg, and OCS…C6H6…Rg (Rg=He, Ne, Ar, and Kr) have been studied by means of MP2calculations and QTAIM analyses. The optimized geometries of the title complexes have C6v symmetry. The intermolecular interactions in the OCS…C6H6…Rg complexes are comparatively stronger than that in the OCS…C6H6complex, which prove that the He, Ne, Ar, and Kr atoms have the ability to form weak bonds with the π bonding electrons of the benzene molecule. In QTAIM studies, the%electron density of benzene was separated from the total electron density, molecular graphs and topological parameters of the OCS…πC6H6, πC6H6…Rg, and OCS…πC6H6…Rg complexes indicate that the interactions are mainly attributed to the electron density provided by the%bonding electrons of benzene and the top regions of the S atom and Rg atom. Charge transfer is obser- ved from the benzene molecule to SCO/Rg in the formation of the OCS…6H6,C6H6…Rg, and OCS…C6H6…Rg complexes. Molecular electrostatic potential (MEP) analyses suggest that electrostatic energy plays a pivotal role in these intermolecular interactions.3. The parallel-shaped complexes OCS…ydrocarbon, CO2…hydrocarbon, and N2O…hydrocarbon (hydrocarbon=ethylene, acetylene, dimethylacetylene) were investigated at the MP2/aug-cc-pVDZ level.The interaction energies are along the sequence of B…C2H4<B…C2H2<B…C4H6(B=OCS, CO2, N2O), and the interaction distances are in sequence of B-C2H4> B-C2H2> B-C4H6(B=OCS, CO2, N2O). The π…π interactions were investigated by using the topological analysis of electron density. The nature of interactions of the parallel-shaped complexes belongs to weak electrostatic interactions. The bond paths in the molecular graphs of π electron density and total electron density show the same orientation, indicating that the π…π interactions play the important role in these intermolecular interactions. NBO analyses showed that charge transfers were observed from C2H4, C2H2, C4H6to OCS, CO2, N2O, and the amount of charge transfer are in sequence of B…C2H4<B…C2H2<B…C4H6(B=OCS,CO2, N2O), which exactly match the order of the interaction energies.The innovations in this thesis:1. In this work, the model of the separation of π…π electron was established, which was implemented procedures and added to the GTA-2010. Using the new procedures, the π electron density function and the contour maps of Laplacian of π electron density were obtained, and the topological properties of this kind of π type interaction could be discussed. The molecular graphs of π electron density were obtained, using the programs AIM2000and GTA-2010. Therefore, the changes of electron density could be described visually and quantificationally.2. The electron localization function (ELF) is a good descriptor of chemical bonding, which has been widely used in atoms, molecules and solid systems. The contour maps of ELF of π electron density were obtained, using the programs TopMod and GTA-2010. Therefore, the orientation and region of electron concentration and electron depletion could be described visually.3. van der Waals complexes involving the benzene molecule, OCS molecule and rare gas atoms (Rg=He, Ne, Ar, and Kr) were firstly observed and analyzed theoretically in this work. And the equilibrium geometries of OCS…C6H6…Rg complexes (Rg=He, Ne, Ar, and Kr) were obtained. This proves that the He, Ne, Ar, and Kr atoms have the ability to form weak bonds with the π bonding electrons of the benzene molecule. 4. The parallel-shaped complexes involving greenhouse gases (OCS, CO2, N2O) and hydrocarbon (C2H4, C2H2, C4H6) were firstly analyzed theoretically in this work. The bond paths in the molecular graphs of%electron density and total electron density show the same orientation, indicating that the π…π interactions play the important role in these intermolecular interactions. |
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