Question 1

What is the difference between a nucleophile and an electrophile?

Accepted Answer

A nucleophile is electron-rich and donates an electron pair to an electrophilic centre. An electrophile is electron-deficient and accepts that electron pair, so a Lewis acid is also an electrophile.

Question 2

Why are NH3, H2O and OH- Lewis bases?

Accepted Answer

Each contains a lone pair that can be donated. Nitrogen has one lone pair in NH3, oxygen has two lone pairs in H2O, and oxygen in OH- has three lone pairs around its single O-H bond, giving OH- its negative formal charge.

Question 3

Why is BF3 an electrophile?

Accepted Answer

Boron in BF3 is surrounded by only six bonding electrons and has an incomplete octet. Its vacant p orbital, perpendicular to the trigonal-planar molecular plane, can accept an electron pair.

Question 4

How should the curved arrow be drawn in a Lewis acid–base reaction?

Accepted Answer

The curved arrow starts at the electron pair of the Lewis base and points toward the Lewis acid. In an NH3–BF3 adduct, it is drawn from the nitrogen lone pair toward boron.

Question 5

Which atom is electrophilic in an alkyl halide?

Accepted Answer

The polar C-X bond makes the carbon atom electron-deficient and therefore electrophilic. A covalently bonded halogen in that molecule should not be labelled a nucleophile, although a separate halide ion can act as one.

Nucleophile and Electrophile: Who Gives and Who Takes?

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