Question

The correct order of lewis acid strength of $B(OH{)}_3$, $B(N{H}_2{)}_3$, $B{F}_3$ and $BC{l}_3$ is:

• A. $B(N{H}_2{)}_3<B(OH{)}_3<B{F}_3<BC{l}_3$
• B. $BC{l}_3<B(OH{)}_3<B(N{H}_2{)}_3<B{F}_3$
• C. $BC{l}_3<B(N{H}_2{)}_3<B(OH{)}_3<B{F}_3$
• D. $B{F}_3<B(OH{)}_3<B(N{H}_2{)}_3=BC{l}_3$

Answer 1

The correct option is A $B(N{H}_2{)}_3<B(OH{)}_3<B{F}_3<BC{l}_3$

Lewis acid - Tendency of a species to accept an electron pair in its empty orbital.
Firs,t check overlapping with the side atom which can donate a pair of electrons
$BC{l}_3$ overlapping is 2p-3p
$B(N{H}_2{)}_3$ overlapping is 2p-2p
$B(OH{)}_3$ overlapping is 2p-2p
$B(F{)}_3$ overlapping is 2p-2p
bond strength 2p-2p>2p-3p, empty orbital of B in $BC{l}_3$ has a high tendency of accepting a pair of electrons from a lewis base.

$B(OH{)}_3$, $B\left(N{H}_2\right)3$ and $B{F}_3$ have same overlapping strength so let's check the electronegativety of the side atom. If the electronegativety of the side atom is high, then the lewis acidic strength of that species will be greater than the others. Among $B(OH{)}_3$, $B\left(N{H}_2\right)3$ and $B{F}_3$, the lewis acidic strength is
$B(N{H}_2{)}_3<B(OH{)}_3<B{F}_3<BC{l}_3$