Nucleophiles are species (neutral or negatively charged) that are attracted to positive sources. The word "nucleophile" is made up of two greek words, nucleo meaning nucleus and philea meaning attracted to or liking. Typical nucleophiles are any negative ion and and neutral atom that has a lone pair to donate like H2O and NH3. Nucleophiles can also be called Lewis bases because they can donate electrons during a chemical reaction. Nucleophiles often enter into substitution type reactions where they take the place of some atom or group of atoms that leave the main molecular system. They can also be a part of an addition reaction involving a C=O group found in several Organic families like aldehydes and ketones. The C=O group also known as the "carbonyl" group will react with nucleophiles in substitution as well especially if there is a strong leaving group attached to the carbonyl initially. Such compounds like carboxylic acids, esters, acid anhydrides, and amides where the there is a group of atoms that leave the carbonyl rather easily.
Sometimes but rarely nucleophiles are involved in a nucleophilic aromatic substitution.
Electrophiles are species (neutral or positively charged) that are attracted to negative sources or electron sources. The word "electrophile" is made up of two greek words elektra meaning electron and phile meaning liking or attracted to. Electrophiles can be any cation such as H3O+ or neutral compounds like BCl3 or AlBr3. Any Lewis acid can act as an electrophile since Lewis acids are attracted to electrons. Electrophiles are involved in electrophilic aliphatic addition such as Chlorination, Hydrochlorination, Hydration, and aqueous Chlorinations. Electrophiles are also involved in Electrophilic Aromatic substitutions where an electrophile takes the place of a hydrogen atom on a Benzenoid or Benzene itself. Examples of these reactions are halogenations (Cl,Br,I), Nitration, Sulfonation, Alkylations, and acylations.
R. H. Logan, Instructor of Chemistry, Dallas County Community College District, North Lake College.
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Revised: 8/20/97
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