Paulings Work and Scope of the Article

Quantum chemical calculations can provide a direct answer to this question and show whether Pauling s arguments are correct. Accordingly, we will discuss the silylium cation problem by focusing on the contribution that Quantum Chemistry can provide in this case. First, we will describe the quantum chemical methods needed for this purpose. Accordingly, Section 2 of this work is devoted to a discussion of the NMR/ab initio/IGLO method and its extension to density functional theory (DFT), namely the NMR/DFT/IGLO method. 

In Sections 3 and 4, the history of the silylium ion problem and the basis for a systematic description of silylium ions in solution are presented. So far, none of the protagonists of the scientific feud on the nature of silylium ions in solution has tried to clarify what is meant by terms such as silylium ion character, free, nearly free, or coordinated silylium ions, degree of complexation, and the type of interactions between solute and solvent. Of course, this has to do with the fact that depending on the experiments performed just one or two properties of the solvated silylium ions can be measured, and this is not sufficient to support basic definitions. However, calculations provide a variety of different silylium ion properties and, thereby, a basis can be established to give a rather conclusive description of silylium ions in solution. 

In Sections 5, 6 and 7, three different approaches to the problem of silylium ions in solution are described. First, the typical gas phase versus solution phase ab initio (DFT) description of silyl compounds and silylium ions is given (Section 5). In Section 6, the NMR/ab initio/IGLO and NMR/DFT/IGLO methods are used to investigate solvation of silylium ions in different solvents. This work demonstrates how complex the solvation process of a silylium ion can be and, therefore, there is a need to generate silylium ions under well-defined situations in solution which simplify investigations. Out of this necessity, the idea of intramolecular solvation of silylium ions was born, which is discussed in Section 7. 

---