In which one of the following molecules strongest back donation of an electron pair from halide to boron is expected?

Question:
In which one of the following molecules strongest back donation of an electron pair from halide to boron is expected?

$\mathrm{BCl}_{3}$
$\mathrm{BF}_{3}$
$\mathrm{BBr}_{3}$
$\mathrm{BI}_{3}$

Correct Option: , 2

Solution:

Type of back bonding

$\mathrm{BF}_{3}$ $\begin{array}{lll}\mathrm{BCl} & \mathrm{BBr}_{3} & \mathrm{BI}_{3}\end{array}$

Therefore back bonding strength is as follows

$\mathrm{BF}_{3}>\mathrm{BCl}>\mathrm{BBr}_{3}>\mathrm{BI}_{3}$

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