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Which of the following molecules acts as a Lewis acid?
A
$(CH_3)_3N$
B
$(CH_3)_3B$
C
$(CH_3)_2O$
D
$(CH_3)_3P$
Detailed Solution
A Lewis acid is a species that can accept a pair of electrons.
In $(CH_3)_3B$, boron forms three bonds and has only six electrons in its valence shell; it has a vacant p orbital and is electron deficient, so it accepts an electron pair.
In $(CH_3)_3N$ and $(CH_3)_3P$ the central atom carries a lone pair, and in $(CH_3)_2O$ oxygen carries two lone pairs; these donate electron pairs and act as Lewis bases.
Hence the molecule that acts as a Lewis acid is $(CH_3)_3B$.
In $(CH_3)_3B$, boron forms three bonds and has only six electrons in its valence shell; it has a vacant p orbital and is electron deficient, so it accepts an electron pair.
In $(CH_3)_3N$ and $(CH_3)_3P$ the central atom carries a lone pair, and in $(CH_3)_2O$ oxygen carries two lone pairs; these donate electron pairs and act as Lewis bases.
Hence the molecule that acts as a Lewis acid is $(CH_3)_3B$.