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Q.
Pick out the incorrect statement.
NTA AbhyasNTA Abhyas 2020Chemical Bonding and Molecular Structure
Solution:
In trimethylamine, 'N' atom is $sp^{3}$ -hybridized.
Due to the presence of lone pair in $sp^{3}$ -hybrid orbital, the geometry of $\left( CH _{3}\right)_{3} N$ becomes pyramidal around nitrogen.
This lone pair of electrons can be donated to electron-deficient species,
e.g., $\left( CH _{3}\right)_{3} N \rightarrow BF _{3}$. This lone pair cannot be transferred to carbon
atom, because carbon atom has no d-orbital in its valence shell. In $\left( SiH _{3}\right)_{3} N ,$ the ' $N ^{\prime}$ atom is $sp ^{2}$ -hybridized.
The orientation of three $sp^{2}$ -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 $p\pi -d\pi $ multiple bonds. Consequently, $\left(S i H_{3}\right)_{3}N$ has no donor properties. For example
$\left( SiH _{3}\right)_{3} N + BF _{3} \rightarrow$ No reaction.