Rotational Spectroscopic Studies On ?-Hole Noncovalent Interactions

?-hole non-covalent interactions play a vital role in molecular recognition,drug design and biological systems.They are not only related to the spatial structure of molecular systems but also the basis for deeply understanding the properties of liquids and solids or crystals.According to the type of?-hole atoms,?-hole non-covalent interactions can be divided into hydrogen bonds,halogen bonds and carbon bonds,etc.Although hydrogen bonds and halogen bonds are mostly well studied,we can further summarize and study the influence of the length of alkyl chain on hydrogen bonds and halogen bonds.In addition,carbon bonds have important applications in supramolecular chemistry,but study on the nature of carbon bonds is very limited,especially the nature of the interaction involved in cyclic compounds and carbonyl compounds formed carbon bonds.Studies on model systems of the?-hole non-covalent interactions at the molecular level can unravel their bonding rules and nature,and provide theoretical references for the study of macroscopic systems.Rotational spectroscopy,as a kind of gas phase spectroscopy that can be free from solvent or lattice strain effects in the condensed phase on the target system,has the characteristic of"fingerprint".It can study?-hole non-covalent interactions from the structure and energy,and then discuss physical origin of the non-covalent interactions at the molecular level.In this paper,a series of model molecules including alkyl amines,perfluoroalkanes,and carbonyl compounds are selected as the research objects.The high-resolution rotational spectroscopy technology combined with quantum chemical calculations is used to study different types of?-hole non-covalent interactions.The researches are as follows:(1)Through high-resolution Fourier transform rotational spectroscopy combined with state-of-the-art quantum-chemical calculations,the studies of?-hole hydrogen bonds in the complexes of n-propylamine and isopropylamine with water are performed,and the semi-experimental structures of the observed 6 isomers are derived.In addition,the quantum chemical calculation methodology is then extended to the study of methylamine-water and ethylamine-water complexes.Analyses of non-covalent interactions,energy decomposition and natural bond orbitals of the series of alkylamine complexes:C_nH_2n+1NH₂(n=1-3).Finally,the influence of length of alkyl chain on the?-hole non-covalent interactions and structures of the complexes are summarized.(2)The rotational spectra of five isotopologues of the chloropentafluoroethane-water complex are investigated.The effect of increasing the length of alkyl chain length on the formation of?-hole halogen bonds in the system is analyzed,and the internal dynamics in complex is discussed.Based on the recorded experimental spectroscopic parameters of multiple isotopologues,the structure and dissociation energy of the complex are derived.The ability of Cl atoms and-CF₃ as halogen bond donor is compared.(3)The difference in the types of?-hole non-covalent interactions formed between3-oxetanone with water and formaldehyde is studied.The ether oxygen of 3-oxetanone prefers to interact with water molecules,forming a?-hole O-H···O strong hydrogen bond,while the carbonyl group of 3-oxetanone links to formaldehyde,forming a C···O carbon bond interaction by using carbonyl group of 3-oxetanone as a carbon bond donor.According to the splitting of the rotational spectra of the 3-oxetanone-formaldehyde complex,the energy barrier of the internal rotation of formaldehyde is estimated to be375(10)cm^-1 using the Meyer's one-dimensional flexible model.Finally,the changes of geometries and electron density of 3-oxetanone molecules before and after the formation of monohydrate are compared.(4)The rotational spectroscopic study of the?-hole non-covalent interactions in microsolvated clusters c-C₄F₈-(H₂O)_1-2 of perfluorocyclobutane(c-C₄F₈)is completed by broadband and narrowband rotational spectrometers.It is the first experimental evdence that proves the sp³ hybridized carbon in the four-membered ring c-C₄F₈ can also be used as a carbon bond donor to participate in the formation of?-hole carbon bonds.Based on the transitions splitting of c-C₄F₈-(H₂O)_1-2,the large amplitude motion that causes the splitting in the two complexes is analyzed.Finally,the influence of microsolvation on the molecular structures of c-C₄F₈ is summarized and the experimental structures of the two complexes are derived.