Chemistry - CHEMICAL BONDING Question with Solution | TestHub

In trimethylamine, 'N' atom is$\mathrm{s}{\mathrm{p}}^3$-hybridized.

Due to the presence of lone pair in$\mathrm{s}{\mathrm{p}}^3$-hybrid orbital, the geometry of$(\mathrm{C}{\mathrm{H}}_3{)}_3\mathrm{N}$becomes pyramidal around nitrogen.

This lone pair of electrons can be donated to electron-deficient species, e.g.,$(\mathrm{C}{\mathrm{H}}_3{)}_3\mathrm{N}\to \mathrm{B}{\mathrm{F}}_3$. This lone pair cannot be transferred to carbon atom, because carbon atom has no d-orbital in its valence shell.
In$(\mathrm{S}\mathrm{i}{\mathrm{H}}_3{)}_3\mathrm{N},$the 'N' atom is$\mathrm{s}{\mathrm{p}}^2$-hybridized.

The orientation of three$\mathrm{s}{\mathrm{p}}^2$-hybrid orbitals is plane-triangular, therefore, the geometry around 'N' becomes plane-triangular. Here the lone pair of electrons is transferred to vacant d-orbitals to each of three silicon atoms forming$\mathrm{p}\mathrm{\pi }-\mathrm{d}\mathrm{\pi }$multiple bonds. Consequently,${\left(\mathrm{S}\mathrm{i}{\mathrm{H}}_3\right)}_3\mathrm{N}$has no donor properties. For example
$(\mathrm{S}\mathrm{i}{\mathrm{H}}_3{)}_3\mathrm{N}+\mathrm{B}{\mathrm{F}}_3\to$No reaction.