nonnucleophile

A nonnucleophile is a chemical species that is a strong base but a poor nucleophile. This means it readily donates a proton (acts as a base) but does not easily donate electrons to form a new bond (does not act as a nucleophile). The key difference lies in the electron density and steric hindrance around the atom that would typically act as the nucleophilic center. Nonnucleophilic bases typically have bulky substituents attached to the basic atom, which sterically hinders their ability to approach and attack an electrophilic center, while still allowing them to abstract a proton.

Common examples of nonnucleophilic bases include potassium tert-butoxide (KOtBu) and lithium diisopropylamide (LDA). These reagents are frequently employed in organic synthesis when a strong base is required to deprotonate a substrate, but nucleophilic attack by the base on the substrate or other molecules in the reaction mixture is undesirable. For instance, in elimination reactions, a nonnucleophilic base can selectively remove a proton to form an alkene without reacting with alkyl halides via substitution. The effectiveness of a base as a nonnucleophile is often inversely related to its nucleophilicity.