In a Lewis acid–base interaction, which statement is exemplified by BF3 accepting an electron pair from NH3?

In a Lewis acid–base interaction, which statement is exemplified by BF3 accepting an electron pair from NH3?

• A. BF3 accepts an electron pair from NH3.
• B. NH3 accepts an electron pair from BF3.
• C. BF3 donates an electron pair.
• D. NH3 donates a proton.

Answer: (A)

In a Lewis acid–base interaction, the base is the electron-pair donor and the acid is the electron-pair acceptor. BF3 is electron-deficient, with an empty orbital on boron, so it acts as a Lewis acid. NH3 has a lone pair on nitrogen that can be donated, so it acts as a Lewis base. When they approach, the lone pair from NH3 is donated into the empty orbital on BF3, forming a B–N bond (a coordinate covalent bond, since both electrons in the bond come from NH3). Therefore, BF3 accepting an electron pair from NH3 correctly describes the situation. The other statements would imply the opposite roles or a proton transfer, which isn’t what happens in this Lewis acid–base interaction.

In a Lewis acid–base interaction, the base is the electron-pair donor and the acid is the electron-pair acceptor. BF3 is electron-deficient, with an empty orbital on boron, so it acts as a Lewis acid. NH3 has a lone pair on nitrogen that can be donated, so it acts as a Lewis base. When they approach, the lone pair from NH3 is donated into the empty orbital on BF3, forming a B–N bond (a coordinate covalent bond, since both electrons in the bond come from NH3). Therefore, BF3 accepting an electron pair from NH3 correctly describes the situation. The other statements would imply the opposite roles or a proton transfer, which isn’t what happens in this Lewis acid–base interaction.