Question

Which of these is the best Lewis acid?

Answer 1

The Lewis Acid-base theory defines acids as species accepting pairs of electrons.

The central boron atom in boron trichloride

BCl3

is electron-deficient, enabling the molecule to accept additional pairs of electrons and act as a Lewis Acid.

Each boron atom forms three single bonds with chlorine atoms with all of its valence electrons, such that there are

2⋅3=6valence electrons available to the boron atom in a

BCl3 molecule.

Answer 2

Explanation:

According to this explanation, the acceptor orbital (empty p orbital) on boron is involved to a greater extent in n bonding in BF3 and BCl3 than in BBr3, the Lewis acidity of BF3 and BCl3 are diminished relative to BBr3. Boron trichloride is expected to be the stronger Lewis acid of the two for two reasons.