Question

The molecule(s) having $p\pi -p\pi$ back bonding among the following is/are:

• A. $BC{l}_3$
• B. $B{F}_3$
• C. $BeC{l}_2$
• D. Both a and b

Answer 1

The correct option is D Both a and b

$B{F}_3$ and $BC{l}_3$ have trigonal planar geometry. There exists $p\pi -p\pi$ back bonding between the vacant $2p$ orbital of $B$ and filled $2p$ orbital of $F$ in $B{F}_3$ and filled $3p$ orbital of $Cl$ in $BC{l}_3$ respectively.

Back bonding does not exist in $BeC{l}_2$. To complete its octet $BeC{l}_2$ exist as polymer.