Acid-base hard-soft

The strength of the complexation is a function of both the donor atom and the metal ion. The solvent medium is also an important factor because solvent molecules that are potential electron donors can compete for the Lewis acid. Qualitative predictions about the strength of donor-acceptor complexation can be made on the basis of the hard-soft-acid-base concept (see Section 1.2.3). The better matched the donor and acceptor, the stronger is the complexation. Scheme 4.3 gives an ordering of hardness and softness for some neutral and ionic Lewis acids and bases. 

STRUCTURE-REACTIVITY RELATIONSHIPS Table 7-15. Examples of Hard-Soft Acid-Bases... 

These phenomena can be explained by the (hard-soft) acid-base principal as follows C=N-OH is a soft base, hence has stronger affinity towards soft basic metal cations than hard metal cations. The strong participation of the N-OH group in complex formation was further confirmed by the results shown for extraction experiments with 5 and 6. 

The concept of hard and soft acids and bases can be used to interpret many trends in chemical reactivity. These trends are summarized in the hard-soft acid-base principle (HSAB principle), an empirical summary of results collected from many chemical reactions studied through decades of research. 

Balance the equation, (b) Identify the elements that change oxidation state, (c) Explain the metathesis portion of the reaction using hard-soft acid-base arguments. 

C21-0023. State the hard-soft acid-base (HSAB) principle. Define and give examples of hard and soft acids and bases. 

The hard-soft acid-base principle is not restricted to the usual types of acid-base reactions. It is a guiding principle that for all types of interactions species of similar electronic character interact best. We have already seen some applications (such as the relative strength of HF and HI) of this principle, which we will continue to call HSAB, but we now consider a number of other types of applications. 

The hard-soft acid-base principle just illustrated is one of the most useful principles in all of chemistry for predicting how many types of interactions occur, ft is not restricted to acid-base interactions, so it is better called the hard-soft interaction principle, ft predicts that hard acids (high charge, small size, low... 

Although sometimes referred to as the hard-soft acid-base theory, it is actually a principle that relates to many types of chemical interactions. It provides a good explanation of why HF is a weak acid. If H+ might potentially interact with either H20 or F, the situation with regard to the preferred bonding mode could be shown as follows ... 

Ho, Tse-Lok (1977). Hard and Soft Acid and Base Principle in Organic Chemistry. Academic Press, New York. The applications of the hard-soft acid base principle to many organic reactions. 

Pearson, R. G. (1963). /. Am. Chem. Soc. 85, 3533. The original publication of the hard-soft acid-base approach by Pearson. 

In Chapter 9, the hard-soft acid-base principle was discussed, and numerous applications of the principle were presented. This principle is also of enormous importance in coordination chemistry. First-row transition metals in high oxidation states have the characteristics of hard Lewis acids (small size and high charge). Consequently, ions such as Cr3+, Fe3+, and Co3+ are hard Lewis acids that bond best to hard Lewis bases. When presented with the opportunity to bond to NH3 or PR3, these metal ions bond better to NH3, which is the harder base. On the other hand, Cd2+ bonds better to PR3 because of the more favorable soft acid-soft base interaction. 

The HSAB concept is the hard-soft acid-base concept. 

Ligand preference and possible coordination geometries of the metal center are important bioinorganic principles. Metal ligand preference is closely related to the hard-soft acid-base nature of metals and their preferred ligands. These are listed in Table 1.7.6... 

Table 1.7 Hard-Soft Acid-Base Classification of Metal Ions and Ligands...

This chapter is intended to provide basic understanding and application of the effect of electric field on the reactivity descriptors. Section 25.2 will focus on the definitions of reactivity descriptors used to understand the chemical reactivity, along with the local hard-soft acid-base (HSAB) semiquantitative model for calculating interaction energy. In Section 25.3, we will discuss specifically the theory behind the effects of external electric field on reactivity descriptors. Some numerical results will be presented in Section 25.4. Along with that in Section 25.5, we would like to discuss the work describing the effect of other perturbation parameters. In Section 25.6, we would present our conclusions and prospects. 

The aim of this chapter is to discuss chemical reactivity and its application in the real world. Chemical reactivity is an established methodology within the realm of density functional theory (DFT). It is an activity index to propose intra- and intermolecular reactivities in materials using DFT within the domain of hard soft acid base (HS AB) principle. This chapter will address the key features of reactivity index, the definition, a short background followed by the aspects, which were developed within the reactivity domain. Finally, some examples mainly to design new materials related to key industrial issues using chemical reactivity index will be described. I wish to show that a simple theory can be state of the art to design new futuristic materials of interest to satisfy industrial needs. 

Ayers, P. W., Parr, R. G., and Pearson, R. G. 2006. Elucidating the hard/soft acid/base principle A perspective based on half-reactions. J. Chem. Phys. 124 194107. 

Classification of biologically important metal ions and ligands according to the hard-soft acid-base concept and their general characteristics... 

In accord with the hard-soft acid-base theory, it is not unexpected that benzimi-dazol-2-ones are alkylated on both the N1- and N3 atoms under mildly basic Iiquiddiquid two-phase conditions [90]. (V-AIkylation of 1-isopropenylbenzimi-dazol-2-ones, followed by treatment with acid, provides a viable route to mono-alkylated derivatives (Scheme 5.21). 

In order to clarify the different behavior of anion 2 and 3 (Scheme 4.10) toward DMC, various anions with different soft/hard character (aliphatic and aromatic amines, alcohoxydes, phenoxides, thiolates) were compared with regard to nucleophilic substitutions on DMC, using different reaction conditions. Results were in good agreement with the hard-soft acid-base (HSAB) theory. Accordingly, the high selectivity of monomethylation of CH2 acidic compounds and primary aromatic amines with DMC can be explained by two different subsequent reactions, which are due to the double electrophilic character of DMC. The first... 

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