Non-nucleophilic base

Non-nucleophilic base

As the name suggests, a non-nucleophilic base is an organic base that is a very strong base but at the same time a poor nucleophile. In thermodynamic reaction control an electron donor molecule acts as a nucleophile, in kinetic reaction control the electron donor abstracts a proton (or rather the proton gets harpooned, hence its alternative name harpoon base). For this reason these bases are said to be involved in kinetic deprotonation.

Non-nucleophilic bases include:

Moderate Basicity (pKa of conjugate acid around 10-13)

High Basicity (pKa of conjugate acid around 17)

Great Basicity (pKA of conjugate acid around 35-40)

The following diagram shows how the hindered base, lithium diisopropylamide, is used to deprotonate an ester to give the enolate in the Claisen ester condensation, instead of undergoing a nucleophilic substitution.

Advantage of LDA.gif

This reaction (deprotonation with LDA) is commonly used to generate enolates.

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