Acceptor solvents, definition general

A1C13, or S02 in an inert solvent cause colour changes in indicators similar to those produced by hydrochloric acid, and these changes are reversed by bases so that titrations can be carried out. Compounds of the type of BF3 are usually described as Lewis acids or electron acceptors. The Lewis bases (e.g. ammonia, pyridine) are virtually identical with the Bransted-Lowry bases. The great disadvantage of the Lewis definition of acids is that, unlike proton-transfer reactions, it is incapable of general quantitative treatment. 

A more general definition of the FCWD includes overlap integrals of quantum nuclear modes. The definition given by Eq. [19] includes only classical solvent modes (superscript s ) for which these overlap integrals are identically equal to unity. An extension of Eq. [19] to the case of quantum intramolecular excitations of the donor-acceptor complex is given below in the section discussing optical Franck-Condon factors. 

A more general definition of acid-base equilibrium in molecular solvents was proposed independently by Brpnsted and Lowry, who extended the term base . According to them, the acid is a donor of protons, and they defined a base only as an acceptor of H+. According to the Brpnsted-Lowry definition, the dissociation of an acid results in the formation of a proton and a conjugate base ... 

Quantitative investigations of the reactions of oxide ions and oxo-compounds in high-temperature ionic solvents are, therefore, of considerable scientific and applied importance. The interactions of such kinds are referred to as acid-base ones, according to Lewis. Since 1939, when Lux proposed a definition of acids as oxide ion acceptors and bases as donors of O2-, such acid-base interactions came to be called oxoacidity . The most general scheme of a Lux acid-base interaction is presented by the following equation ... 

The Lewis definitions of acid-base interactions are now over a half a century old. Nevertheless they are always useful and have broadened their meaning and applications, covering concepts such as bond-formation, central atom-ligand interactions, electrophilic-nucleophilic reagents, cationic-anionic reagents, charge transfer complex formation, donor-acceptor reactions, etc. In 1923 Lewis reviewed and extensively elaborated the theory of the electron-pair bond, which he had first proposed in 1916. In this small volume which had since become a classic, Lewis independently proposed both the proton and generalized solvent-system definitions of acids and bases. He wrote ... 

A more general definition was suggested independently by Bronsted and Lowry . Proton-transfer reactions are considered as responsible for boijh the self-ionization of the amphoteric solvent molecules and for most acid-base reactions in their solutions. Acids and bases are defined as proton donors and proton acceptors respectively and acid-base reactions are regarded as being due to proton transfer reactions (protolysis). The most significant difference from the Arrhenius definition is that the proton itself is neither acid nor base. Even the solvent molecules can act either as acids or bases, a phenomenon which is responsible for the autoprotolysis of the pure liquid solvents. 

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