(1) Back bonding extent in boron tri halides decreases from
BF3 to BI3 because on increasing of size of
p-orbital of halogens atom the strength of back bond decreases thus extent of back bonding:
Hence it is clear that BF3 is weakest Lewis acid
due to stronger 2pπ-2pπ back bonding (stronger partial double bond character)
in BF3 (lone pair orbital of fluorine into vacant orbital of
boron) and consequently behaves as less electron deficient. The back bonding
gradually decreases (From BF3 to BI3) and becomes
weakest in BI3. So that BI3 become strong Lewis acid
(3) The nucleophilicity(affinity towards nucleophile/water) order is
inversely proportional to the Lewis acid character thus
the nucleophilicity order is:
Related Questions:
Why aqueous solution of AlCl3 is acidic in nature ?
What happen when aq AlCl3 react with Acid or Base?
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B-F bond length in BF3 is shorter than B-F bond length in (BF4)- why?
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Four-center two-electron bond (4C-2e Bond): Structure of AlCl3:
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