Structures and Spectroscopic Properties of Complexes Formed by Oligomers of Siloxanes with Several Phenol Acetates

In order to simulate the weak interaction between guest molecular and stationary phase in gas chromatography (GC), the properties for oligomers of siloxanes with different polymerization degrees are studied. The oligomer of siloxane with polymerization degree 3 is used as host, chlorophenol acetates, tribromophenol acetate and trimethylphenol acetate are used as guests. Six complexes are designed in the 1:1 molar radio by host to guests. The properties of several hosts and complexes are calculated using density functional theory. The higher binding energies of the complexes lead to longer experimental retention times of the guests. The chemical shifts by NMR of the C atoms in the methyl groups at the end of the Si—O chains of the complexes locate at upfield compared with the same C atoms from the hosts. The aromaticities of the benzene rings in the complexes in comparison to the same benzene rings from the hosts increase, owning to the increase of electron clouds density on the benzene rings adjacent to the O atom on the Si—O chains. The calculated results on binding energies and energy gaps of the complexes are in strong relation to the experimental retention time of the guests, and thus this calculation model is reliable and reasonable for describing and predicting the sequence of retention time for the guests. Besides, it can also be used for the theoretical description of the spectroscopic properties for the complexes.