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. 'Hard' applies to species which are small, have high charge states (the charge criterion applies mainly to acids, to a lesser extent to bases), and are weakly polarizable. 'Soft' applies to species which are big, have low charge states and are strongly polarizable.[1]
The theory is used in contexts where a qualitative, rather than quantitative, description would help in understanding the predominant factors which drive chemical properties and reactions. This is especially so in transition metal chemistry, where numerous experiments have been done to determine the relative ordering of ligands and transition metal ions in terms of their hardness and softness.
HSAB theory is also useful in predicting the products of metathesis reactions. In 2005 it was shown that even the sensitivity and performance of explosive materials can be explained on basis of HSAB theory.[2]
Ralph Pearson introduced the HSAB principle in the early 1960s[3][4][5] as an attempt to unify inorganic and organic reaction chemistry.[6]
^Jolly, W. L. (1984). Modern Inorganic Chemistry. New York: McGraw-Hill. ISBN 978-0-07-032760-3.
^[1] E.-C. Koch, Acid-Base Interactions in Energetic Materials: I. The Hard and Soft Acids and Bases (HSAB) Principle-Insights to Reactivity and Sensitivity of Energetic Materials, Prop.,Expl.,Pyrotech. 302005, 5
^Pearson, Ralph G. (1963). "Hard and Soft Acids and Bases". J. Am. Chem. Soc.85 (22): 3533–3539. doi:10.1021/ja00905a001.
^Pearson, Ralph G. (1968). "Hard and soft acids and bases, HSAB, part 1: Fundamental principles". J. Chem. Educ.1968 (45): 581–586. Bibcode:1968JChEd..45..581P. doi:10.1021/ed045p581.
^Pearson, Ralph G. (1968). "Hard and soft acids and bases, HSAB, part II: Underlying theories". J. Chem. Educ.1968 (45): 643–648. Bibcode:1968JChEd..45..643P. doi:10.1021/ed045p643.
^[2] R. G. Pearson, Chemical Hardness – Applications From Molecules to Solids, Wiley-VCH, Weinheim, 1997, 198 pp
of explosive materials can be explained on basis of HSABtheory. Ralph Pearson introduced the HSAB principle in the early 1960s as an attempt to unify...
Marcus theory — Lewis theory (successor to Brønsted–Lowry acid–base theory) — HSABtheory — Debye–Hückel theory — Thermodynamic theory of polymer elasticity...
Brønsted–Lowry acid. The classification into hard and soft acids and bases (HSABtheory) followed in 1963. The strength of Lewis acid-base interactions, as measured...
choice of reactants is guided by a solubility chart or lattice energy. HSABtheory can also be used to predict the products of a metathesis reaction. Salt...
at least two properties must be considered. For Pearson qualitative HSABtheory, the two properties are hardness and strength, while for Drago's quantitative...
strength at least two properties must be considered. For the qualitative HSABtheory the two properties are hardness and strength while for the quantitative...
referred to as a Lewis base. As a refinement of acid-base interactions, the HSABtheory takes into account polarizability and size of ions. Subdivisions of inorganic...
containing ligating atoms other than the lightest of their Periodic Group." HSABtheory, hard and soft (Lewis) acids and bases Weisstein, Eric Wolfgang (ed.)...
polarisability, allow GaCl3 to behave as a "soft acid" in terms of the HSABtheory. The strength of the bonds between gallium halides and ligands have been...
reaction. This quantitative model is often discussed with the qualitative HSABtheory, which also seeks to rationalize the behavior of diverse acids and bases...
so strongly with mercury compounds. According to hard/soft acid/base (HSAB) theory, sulfur is a relatively soft (polarizable) atom. This explains the tendency...
(ISBN 978-0471035589). A qualitative theory of hard and soft acids and bases (HSAB) was proposed in 1963 in an attempt to unify the theories of reactivity in inorganic...
4-addition is suppressed. The selectivity can be explained in terms of the HSABtheory: carbonyl groups require hard nucleophiles for 1,2-addition. The hardness...
at least two properties must be considered. For Pearson's qualitative HSABtheory the two properties are hardness and strength while for Drago's quantitative...
phosphines than with amines. Later, Pearson proposed the theory of hard and soft acids and bases (HSABtheory). In this classification, class A metals are hard...
Lewis acids such as I2, phenol, and Al(CH3)3. Ammonia is a hard base (HSABtheory) and its E & C parameters are EB = 2.31 and CB = 2.04. Its relative donor...
the hydroperoxide anion. In 1962, Edwards and Pearson (the latter of HSABtheory) introduced the phrase alpha effect for this anomaly. He offered the...
often stated to be related to the hardness of the element, within the HSABtheory (hard and soft (Lewis) acids and bases), but it has been shown that oxophilicity...
oxygen or nitrogen than with second-row sulfur or phosphorus. In terms of HSABtheory Zn2+ is a hard acid. In aqueous solution an octahedral complex, [Zn(H2O)6]2+...
a pseudohalide (X). Carboxylates are classified as hard ligands, in HSABtheory. Structures of Selected Metal Acetates Basic ferric acetate Silver acetate...
bonds between the electron pair donors and the hydrogen atoms of water. HSABtheory describes water as both a weak hard acid and a weak hard base, meaning...
O-bonded is an "L-X ligand", akin to bidentate carboxylate. With respect to HSABtheory, the N bonding mode is more common for softer metal centers. The O and...
development of coordination chemistry. Hard metal cations, as classified by HSABtheory, tend to form N-bonded complexes (isothiocyanates), whereas class B or...
explain the different behavior of the intermediate. In terms of the HSAB-theory an explanation might be given. In 1975 Masamune calculated in the non-substituted...
Inorganic chemist; developed the concept of hard and soft acids and bases (HSABtheory) Born in Chicago Dwight H. Perkins Mar 26, 1867 Nov 2, 1941 Architect...
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