Question

Among the following compounds of Boron, the species which also forms $\pi$ - bond in addition to $\sigma$ - bonds is:

• A. $B{F}_4^{-}$
• B. $B{H}_3$
• C. $B_2{H}_6$
• D. $B{F}_3$

Answer 1

Answer: (D)

$B{F}_3$ show back-bonding via formation of $\pi$ -bond due to :

(i) presence of vacant orbital $(2p)$ in boron element and lone pair of electrons available in $2p$ orbital of fluorine element.

(ii) Due to small size of boron and fluorine atoms, $\pi$ -bond (a back bond) is formed in addition to \sigma-bond between $B$ and $F$ atoms.