{{Short description|Sterically hindered organic base}} {{Acids and bases}} As the name suggests, a '''non-nucleophilic base''' is a sterically hindered organic base that is a poor nucleophile. Normal bases are also nucleophiles, but often chemists seek the proton-removing ability of a base without any other functions. Typical non-nucleophilic bases are bulky, such that protons can attach to the basic center but alkylation and complexation is inhibited.
==Non-nucleophilic bases== A variety of amines and nitrogen heterocycles are useful bases of moderate strength (pK<sub>a</sub> of conjugate acid around 10-13) *''N'',''N''-Diisopropylethylamine (DIPEA, also called Hünig's Base<ref>K. L. Sorgi, "Diisopropylethylamine," Encyclopedia of Reagents for Organic Synthesis, 2001. {{doi|10.1002/047084289X.rd254}}</ref>), pK<sub>a</sub> = 10.75 *1,8-Diazabicycloundec-7-ene (DBU) - useful for E2 elimination reactions, pK<sub>a</sub> = 13.5 *1,5-Diazabicyclo(4.3.0)non-5-ene (DBN) - comparable to DBU *2,6-Di-tert-butylpyridine, a weak non-nucleophilic base<ref>Rafael R. Kostikov, Sánchez-Sancho Francisco, María Garranzo and M. Carmen Murcia "2,6-Di-t-butylpyridine" Encyclopedia of Reagents for Organic Synthesis 2010. {{doi|10.1002/047084289X.rd068.pub2}}</ref> pK<sub>a</sub> = 3.58 *Phosphazene bases, such as ''t''-Bu-P<sub>4</sub><ref>''Activation in anionic polymerization: Why phosphazene bases are very exciting promoters'' S. Boileau, N. Illy Prog. Polym. Sci., '''2011''', 36, 1132-1151, {{doi|10.1016/j.progpolymsci.2011.05.005}}</ref>
Non-nucleophilic bases of high strength are usually anions. For these species, the pK<sub>a</sub>s of the conjugate acids are around 35–40. * Lithium diisopropylamide (LDA), pK<sub>a</sub> = 36 * Silicon-based amides, such as sodium and potassium bis(trimethylsilyl)amide (NaHMDS and KHMDS, respectively) * Lithium tetramethylpiperidide (LiTMP or harpoon base) Other strong non-nucleophilic bases are sodium hydride and potassium hydride. These compounds are dense, salt-like materials that are insoluble and operate by surface reactions.
Some reagents are of high basicity (pK<sub>a</sub> of conjugate acid around 17) but of modest but not negligible nucleophilicity. Examples include sodium ''tert''-butoxide and potassium ''tert''-butoxide.
==Example== 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.
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This reaction (deprotonation with LDA) is commonly used to generate enolates.
==References== <references/>
Category:Non-nucleophilic bases