What are nucleophiles, electrophiles, acids, and bases, and how should they be used in chemical synthesis?

Answer 1

"phile" means "lover of" in Greek, such as a bibliophile "lover of books" for example.

Knowing that, understand that a nucleophile is a molecule that has a strong tendency to attack a molecular "nucleus" or site that wants to be attacked, especially a part of a molecule that lacks electrons. This site of the molecule wants electrons and therefore is electrophilic. This molecule is the electrophile. It is not uncommon for the nucleophile to have a high electron density and in some cases such as KCN (-CN) is negatively charged. The rule holds true for electrophiles as well which are often positive as a consequence of their desire to receive electrons.

In an Sn2 reaction, the reagent that the arrow comes from is the nucleophile. The arrowhead is going to the electrophile, the molecule being attacked. As a result of this substitutive attack, the leaving group is bumped off in a one step, 2 arrow, reaction.

Acids and Bases are defined differently by Lewis and by Brønsted-Lowry. The latter says that an acid donates a proton (H+) such as H3O+ being the acid that donates a proton to become H2O, it's conjugate base. A base, by this definition is the proton recipient such as -OH becoming it's conjugate acid, H2O.

Lewis acids and bases concern the donation and receipt of electron pairs. Lewis bases are electron pair donors and lewis acids are electron pair recipients (just think opposite of Bronsted Lowry, but the same thing is being said in a different way because Lewis is talking about electron pairs, the movement of which is shown by curved arrows we draw, whereas Bronsted Lowry is talking about the gain or loss of an H+).