Non-nucleophilic base: Difference between revisions
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Non-nucleophilic bases include: |
Non-nucleophilic bases include: |
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Moderate Basicity (pKa of conjugate acid around 10-13) |
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*[[Triethylamine]], or TEA |
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*Diisopropylethylamine, or DIPEA |
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*[[1,8-Diazabicycloundec-7-ene]], or DBU -- a favorite for the E2 [[elimination reaction]]. |
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High Basicity (pKa of conjugate acid around 17) |
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* Sodium tert-butoxide |
* Sodium tert-butoxide |
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* Potassium tert-butoxide |
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Great Basicity (pKA of conjugate acid around 35-40) |
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The following diagram shows how the hindered base, lithium diisopropylamide, is used to form to deprotonate an ester to give the enolate in the [[Claisen condensation|Claisen ester condensation]], instead of undergoing a nucleophilic substitution. |
The following diagram shows how the hindered base, lithium diisopropylamide, is used to form to deprotonate an ester to give the enolate in the [[Claisen condensation|Claisen ester condensation]], instead of undergoing a nucleophilic substitution. |
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Revision as of 19:17, 5 November 2009
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)
- Triethylamine, or TEA
- Diisopropylethylamine, or DIPEA
- 1,8-Diazabicycloundec-7-ene, or DBU -- a favorite for the E2 elimination reaction.
High Basicity (pKa of conjugate acid around 17)
- Sodium tert-butoxide
- Potassium tert-butoxide
Great Basicity (pKA of conjugate acid around 35-40)
- Lithium diisopropylamide, or LDA
- Silicon-based amides, such as sodium and potassium bis(trimethylsilyl)amide (NaHMDS and KHMDS respectively)
- Lithium tetramethylpiperidide, or LiTMP
The following diagram shows how the hindered base, lithium diisopropylamide, is used to form to deprotonate an ester to give the enolate in the Claisen ester condensation, instead of undergoing a nucleophilic substitution.
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