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The Concept of Hard and Soft Acids and Bases as Applied to Multi‐Center Chemical Reactions
Author(s) -
Saville B.
Publication year - 1967
Publication title -
angewandte chemie international edition in english
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 0570-0833
DOI - 10.1002/anie.196709281
Subject(s) - hsab theory , electrophile , nucleophile , lewis acids and bases , chemistry , base (topology) , interpretation (philosophy) , ion , molecule , acid–base reaction , acceptor , chemical bond , computational chemistry , organic chemistry , catalysis , computer science , mathematics , physics , mathematical analysis , programming language , condensed matter physics
Many chemical bonds of differing types and strengths have recently been regarded by Pearson [1] as representing partnerships between (Lewis) acids and (Lewis) bases. Most acceptor molecules or ions (acids) can be placed in one or other of two categories, graphically termed “Hard” and “Soft”. There are also two broad categories of donor molecules or ions (bases) which can also be termed Hard and Soft. On the whole, strong chemical bonds are partnerships between either a Hard base and a Hard acid or a Soft base and Soft acid, whereas weaker bond types most usually result in cases of either Hard base‐Soft acid or Soft base‐Hard acid interactions. The present paper shows how this concept of acidity and basicity can be applied in the interpretation of multi‐center chemical reactions involving interconnected acid‐base relationships. In particular, fourcenter substitutions and additions involving cooperative attack by nucleophiles and electrophiles at various chemical bonds have been examined, and a conclusion is reached that especially reactive patterns of reactants can be developed if the substrates contain bonds between either a hard acid and a soft base, or a soft acid and a hard base. Indeed, the arguments can be elaborated to provide two distinct Rules which should be of interest in the interpretation of metal‐ion assisted reactions and in the design of novel syntheses.