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Thanks decreasing order of power of boron halides to act as Lewis acids is ?

Thanks decreasing order of power of boron halides to act as Lewis acids is ?

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2 Answers

Arun
25750 Points
4 years ago
BI3>BBr3>BCl3>BF3.this trend is due to pie back bonding. All halides have lone pairs, they donate one lone pair to boron by overlapping with the p orbital of ..
Vikas TU
14149 Points
4 years ago
Dear student 
We know that the electronegativity of halogens decreases from fluorine to iodine as we move down the group. Hence, according to this, BF 3 should be the most Lewis acidic due to the electron withdrawing nature of fluorine atoms.
However, the order is just the opposite due to back-bonding. Back bonding due to the lone pair of electrons of halogen atom increases electron density on B centre, thereby, reducing its lewis acid character. This back bonding is more in case of BF3 due to similar size of orbitals of boron and fluorine atoms, whereas it decreases down the group due to the increasing size of orbitals as we move from F to I.

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