Rotational Studies On Weak Intermolecular Interactions Between Nitrogen Heterocyclic Rings And CO₂

The essence of carbon dioxide(CO₂)adsorption by organic amine adsorption materials is weak intermolecular interactions between organic amines and CO₂.From the molecular level,studying sites and types of weak intermolecular interactions between organic amines and CO₂ molecules and revealing bonding rules and molecular structure are the basis for in-depth understanding of the mechanism of CO₂ adsorption and of great significance for optimizing the design of new materials and methods for capturing CO₂.High-resolution Fourier transform microwave spectroscopy combined with theoretical calculation is effective in studying of weak intermolecular interactions.Accurate structural parameters,conformational equilibrium relationship and internal dynamics process can be provided,free from the interference of solvent molecular forces or lattice constrains in condensed phases.Nitrogen heterocyclic rings are often used as structural units to prepare capture materials due to their high binding energy with CO₂.In this paper,three representative of nitrogen heterocyclic rings,pyrrole,pyrrolidine and morpholine are chosen to form complexes with CO₂,respectively,as the research object.The self-developed pulsed supersonic jet Fourier transform microwave spectrum technique combined with the quantum chemical calculation was employed to collect the rotation spectrum of the target compound,analyze the accurate structure,conformational balance and bonding patterns of intermolecular weak interaction.The change of binding sites between CO₂ and nitrogen heterocyclic rings in different environments with the change of electron density are revealed.The main contents of each chapter of this paper were as follows:The first chapter briefly introduced the research background.The types of common weak intermolecular interactions were outlined,and the interaction sites,the possible binding modes and types of interactions between CO₂ and organic amines are summarized as well.The conformational balance existing in molecular complexes was explained.Then,the current research status of the rotational spectroscopy of the complex formed by organic amines and CO₂ is summarized.Finally,the research objectives and contents of this paper are introduced.The second chapter summarized the basic principles of rotational spectroscopy.Molecular and structural types,rotational transitions and nuclear quadrupole coupling effects and the working principles of microwave spectrometers were briefly described.The third to fifth chapters were the experimental parts.The rotational spectrum of pyrrole,pyrrolidine and morpholine forming complexes with CO₂ were obtained by pulsed supersonic jet Fourier transform microwave spectroscopy in the frequency range of 2-20 GHz,meanwhile combing quantitative calculation,the conformation,energy ordering and structure of complex were studied in detail.In addition,rotational spectrum of the mono-substituted ¹³C and ¹⁵N isotopologues of preferred conformation in the complex were also measured under the natural abundance according to the intensity of the line,enabling the accurate structural description of the carbon skeleton.At the same time,some theoretical analysis methods were used to visualize weak intermolecular interactions in conformation and quantitatively analyze the strength of weak intermolecular interactions.The sixth chapter was the summary and prospect of this paper.From the conformational change of monomers to the conformational equilibrium of forming complexes,from the possible types of interactions that might exist in complex to the competition for conformational stability,the innovation points of the research contents were pointed out,and the choice of different theoretical calculation methods and other nitrogen heterocyclic rings were prospected.