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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 ...
Hard metal cations, as classified by HSAB theory, tend to form N-bonded complexes (isothiocyanates), whereas class B or soft metal cations tend to form S-bonded thiocyanate complexes. For the isothiocyanates, the M-N-C angle is usually close to 180°. For the thiocyanates, the M-S-C angle is usually close to 100°.
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.
[2] [17] The Brønsted–Lowry acid–base theory was published in the same year. The two theories are distinct but complementary. A Lewis base is also a Brønsted–Lowry base, but a Lewis acid does not need to be a Brønsted–Lowry acid. The classification into hard and soft acids and bases (HSAB theory) followed in 1963.
HSAB theory can also be used to predict the products of a metathesis reaction. Salt metathesis is often employed to obtain salts that are soluble in organic solvents. Illustrative is the conversion of sodium perrhenate to the tetrabutylammonium salt: [2] NaReO 4 + N(C 4 H 9) 4 Cl → N(C 4 H 9) 4 [ReO 4] + NaCl
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 and organic chemistry. [4] In this theory 'Hard' applies to species that are small, have high charge states, and are weakly polarizable. 'Soft' applies to species that are large, have low charge states ...
In the theory of chemical reactivity, the Klopman–Salem equation describes the energetic change that occurs when two species approach each other in the course of a reaction and begin to interact, as their associated molecular orbitals begin to overlap with each other and atoms bearing partial charges begin to experience attractive or repulsive electrostatic forces.
In 1962, Edwards and Pearson (the latter of HSAB theory) introduced the phrase alpha effect for this anomaly. He offered the suggestion that the effect was caused by a transition state (TS) stabilization effect: on entering the TS the free electron pair on the nucleophile moves away from the nucleus, causing a partial positive charge which can be stabilized by an adjacent lone pair as for ...