Question

The geometry of $N$ in Silyl isocyanate $\left(Si{H}_{3}NCO\right)$ and Methyl isocyanate $\left(C{H}_{3}NCO\right)$ repectively is:

• A. Linear and Bent
• B. Bent and Linear
• C. Pyramidal and Linear
• D. Linear and Linear

Answer 1

The correct option is A Linear and Bent

In Silyl isocyanate and methyl isocyanate, the central atom $\left(N\right)$ has a lone pair of electrons and two sigma bond pairs. Hence, both should be $s{p}^2$ hybridised and should have trigonal planer shape. But in Silyl isocyanate, the lone pair of $N$ is forming back bond with the vacant $d$ orbital of $Si$ i.e. $d\pi -p\pi$ back bonding and its shape becomes linear.

In methyl isocyanate, $C$ does not have any vacant $d$ orbital for back bonding and thus the $N$ atom with the lone pair is $s{p}^2$ hybridised. Hence, its shape is bent.