Question

Which of the following molecules has large extent of back bonding?

• A. $O(Si{H}_3{)}_2$
• B. $O{I}_2$
• C. $NC{l}_3$
• D. All have same extent

Answer 1

The correct option is A $O(Si{H}_3{)}_2$

a) In $O(Si{H}_3{)}_2$, oxygen has a lone pair in $p$-orbital and $Si$ has vacant d-orbitals. So, $O(Si{H}_3{)}_2$ has $2p\pi -3d\pi$ back bonding.
b) In $O{I}_2$ oxygen has a lone pair in $p$-orbital and $I$ have a vacant $5d$-orbital. Hence,due to large size difference it has poor overlapping as compared to $O(Si{H}_3{)}_2$.
c) In $NC{l}_3$ there is no back bonding due to less electronegativity difference of Nitrogen and Chlorine.
Hence, $O(Si{H}_3{)}_2$ has the maximum extent of overlapping.