化学专业英语翻译^Electron dot formulas clarify the mechanism of forming a coordinate bond in the neutralization of a Lewis acid. Neutralization of a proton by an ammonia molecule is A The acid — base pair Al3+ and H2O undergoes Lewis neutralization by forming
2019-04-20
化学专业英语翻译^
Electron dot formulas clarify the mechanism of forming a coordinate bond in the neutralization of a Lewis acid. Neutralization of a proton by an ammonia molecule is A
The acid — base pair Al3+ and H2O undergoes Lewis neutralization by forming six coordinate bonds.
Many displacement reactions illustrate the relative strength of the Lewis acid or base. For example, the cyanide ion is a stronger base than the fluoride ion by virtue of its ability to displace the fluoride ion from the hexafluoroferrate (III) ion: FeF63- + 6CN- ------→ Fe(CN)63- + 6F-
There are many reactions that fit the Lewis acid-base concept. In contrast to proton loss or gain in the Bronsted-Lowry concept, the Lewis concept emphasizes the electron pair ------a Lewis acid lacks an electron pair in an empty orbital, or has an orbital that can be vacated and a Lewis base has a nonbonding electron pair and can supply this pair to another substance lacking an electron pair.
It is evident that the Lewis concept applies, not only to the chemical behavior correlated by the Bronsted-Lowry concept, but also to many chemical reactions that do not involve proton transfer, and for this reason it is most useful. Its generality precludes the establishment of a scale of acid and base strengths for all Lewis acids and bases, but comparisons can be made between selected substances.
The terms nucleophilic, and electrophilic are sometimes applied to bases and acids. Lewis acids that accept an electron pair are electrophilic, and the strength of Lewis bases is measured by their tendencies to supply electrons. For example,H2O is a stronger base than Cl- because H2O displaces Cl~ in supplying an electron pair for the proton:
HCl+H2O------→H3O+ + Cl-
Consequently , H2O is a stronger nucleophilic agent than Cl-.
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