For example
Others examples of Lewis acid-base neutralization.
Lewis acids:
(1) Cations are act as Lewis acids
example, H+ , Ag+ , Cu+2 , Na+ , Fe+2
, Hg+2 etc.
(2) Electron deficient compounds are act
as Lewis acids for examples BF3 ,ACl3
,BCl3 ,FeCl3 etc
(3) The compounds which
central atom with available vacant d-orbital can add additional pairs of electrons even
though it already has an octet or more of electrons act as Lewis acids for
examples SiCl4,PCl5, SOF4,
SbCl3, SbF5 ,SnCl4, IF7, SF4
etc
(4) Compounds containing multiple bonds for example CO2
, SO2, SO3 ,CS2 etc.
Lewis bases:
(1) Anions are act as Lewis base H- ,CH3-
,NH2- , OH- , X- etc. but all the anions are
not Lewis base for example (PCl5)-
(2) The Neutral molecules having lone pairs of electrons act as
Lewis base for examples NH3 ,R-NH2, R-NH-R,
R3-N, H2O , R-OH ,R-O-R , PH3, R-PH2
, R2PH ,R3P , H2S , R-SH , R-S-R etc
(3) Compounds with non polar multiples bond are also act
as Lewis base, example Alkenes(C2H4) , Alkynes(C2H2
) Dienes, polyenes, benzene, Polynuclear homoaromatic compounds. (Ligand in
coordination compounds)
Chemical Reactions according Lewis acid-base concept:
We can now write equations for many reactions that involve a Lewis acid
reacting with a Lewis base. The following are a few examples:
Acid-base behavior according to the Lewis theory has many of the same aspects as does acid-base theory according to the Brønsted–Lowry theory.
(1)There is no acid without a base.
An electron pair must be donated to one species (the acid) by another (the
base).
(2) An acid (or base) reacts to
displace a weaker acid (or base) from a compound.
(3)The interaction of a Lewis acid with a Lewis base is a type of neutralization reaction because the acidic and basic characters of the reactants are removed.
An acid-base
reaction takes place readily between BF3 and NH3 ,
BF3 +NH3 → H3N:BF3
However,
when the product of this reaction is brought into contact with BCl3,
a reaction takes place:
H3N:BF3
+BCl3 → H3N:BCl3 + BF3
In this reaction, a Lewis acid, BF3 , has been replaced by essentially a stronger one BCl3 . And replacement of Lewis acid by other Lewis acid follow Second order Nucleophilic substitution (SN2).
Merits of Lewis concept:
(1) The acid/base nature of substance may also defined without
any solvent.
(2) It is highly useful to explain coordination compounds in
which central metal atom into behave as Lewis acid and ligands behave as Lewis
base.
(3) The acid having greater tendency to accept lone pair bare
stronger acid and base have greater tendency to donate lone pair are stronger
base.
Demerites of Lewis concept:
(1) It is extremely generalized Concept , almost all the
compounds either become acid or base by this Concept.
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