Quantum chemical calculations and IR spectra of (O—Si)-chelate N-(fluorosilyl)methyl-N-isopropylureas

Abstract

Quantum chemical calculations of (O—Si)-chelate N-(fluorosilyl)methyl-N-isopropyl-N′, N′-dimethyl- and N-(fluorosilyl)methyl-N-isopropyl-N′, N′-diphenylureas by DFT in the gas phase and in a polar DMSO medium showed the dependence of the geometric parameters of their molecules on the stereoelectronic effects of substituents at the silicon and nitrogen atoms and the polarity of the medium. The nature of the Si—O and Si—F bonds of the axial fragment of the coordination site was determined using the analysis of the topological characteristics of the bond critical points and the determination of their energy values within the framework of the quantum theory of atoms in molecules (QTAIM); NBO analysis (NBO is natural bond orbital) of orbital interactions of the LEP of the N and O atoms and the vacant orbitals of the C=O and C—N bonds showed their dependence on the polarity of the medium. A comparison of the experimental and calculated IR spectra of the studied compounds in the solid state and polar medium indicates an inversion of the v_as frequencies characterizing the vibrations of the O=C—N(1) carbonyl group and the N(1)—C—N(2) fragment in N-(trifluorosilyl)methyl-N-isopropyl-N′, N′-dimethylurea.