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HSAB is an acronym for "hard and soft (Lewis) acids and bases". HSAB is widely used in chemistry for explaining the stability of compounds , reaction mechanisms and pathways. It assigns the terms 'hard' or 'soft', and 'acid' or 'base' to chemical species .
The classification into hard and soft acids and bases (HSAB theory) followed in 1963. The strength of Lewis acid-base interactions, as measured by the standard enthalpy of formation of an adduct can be predicted by the Drago–Wayland two-parameter equation.
In chemistry, an acid–base reaction is a chemical reaction that occurs between an acid and a base.It can be used to determine pH via titration.Several theoretical frameworks provide alternative conceptions of the reaction mechanisms and their application in solving related problems; these are called the acid–base theories, for example, Brønsted–Lowry acid–base theory.
For example, Ni 2+ forms stronger complexes with amines than with phosphines, but Pd 2+ forms stronger complexes with phosphines than with amines. Later, Pearson proposed the theory of hard and soft acids and bases (HSAB theory). [27] In this classification, class A metals are hard acids and class B metals are soft acids.
Ralph Gottfrid Pearson (January 12, 1919 – October 12, 2022) was an American physical inorganic chemist best known for the development of the concept of hard and soft acids and bases (HSAB). He received his Ph.D. in physical chemistry in 1943 from Northwestern University , and taught chemistry at Northwestern faculty from 1946 until 1976 ...
First described independently by Gilles Klopman [1] and Lionel Salem [2] in 1968, this relationship provides a mathematical basis for the key assumptions of frontier molecular orbital theory (i.e., theory of HOMO–LUMO interactions) and hard soft acid base (HSAB) theory. Conceptually, it highlights the importance of considering both ...
Oxophilicity is often stated to be related to the hardness of the element, within the HSAB theory (hard and soft (Lewis) acids and bases), but it has been shown that oxophilicity depends more on the electronegativity and effective nuclear charge of the element than on its hardness. [1]
According to the original formulation of Lewis, when a neutral base forms a bond with a neutral acid, a condition of electric stress occurs. [7] The acid and the base share the electron pair that formerly belonged to the base. [7] As a result, a high dipole moment is created, which can only be decreased to zero by rearranging the molecules. [7]