Nucleophiles and Electrophiles

Electrophiles and Lewis Acids

An electrophile is a molecule that forms a bond to its reaction partner (the nucleophile) by accepting both bonding electrons from that reaction partner. Electrophilic reagents are Lewis acids. You've already seen that carbon dioxide is an electrophile.

Below are some examples of electrophiles.

Nucleophiles and Lewis Bases

A nucleophile is a molecule that forms a bond with its reaction partner (the electrophile) by donating both electrons for that bond. Nucleophiles are Lewis bases. As you've seen, hydroxide is an example of nucleophile that adds to carbon dioxide.

Below are some examples of nucleophiles.

Addition of Nucleophiles to the Carbonyl Group

Hydroxide, a nucleophile, adds to the electrophilic carbon of CO2. The purple arrows indicate the migration of a pair of electrons. First a pair of electrons moves from the nucleophile (hydroxide) to the electrophile (carbonyl carbon). Because carbon can't have more than 8 total electrons around it, a pair of electrons associated with the C=O unit must move to the oxygen atom.

Similarly, alcohols are nucleophiles that can add to the electrophilic carbon of an aldehyde.

After the addition of the nucleophile to the electrophile, there is an acid/base reaction. The acidic proton on the positively charged oxygen transfers to the basic, negatively charged oxygen.

Professor Patricia Shapley, University of Illinois, 2012