Editing Lewis acids and bases (section)

==Lewis bases==
A Lewis base is an atomic or molecular species where the [[HOMO|highest occupied molecular orbital]] (HOMO) is highly localized. Typical Lewis bases are conventional [[amine]]s such as ammonia and [[alkyl]] amines. Other common Lewis bases include [[pyridine]] and its derivatives. They are nucleophilic in nature.

Some of the main classes of Lewis bases are:
*amines of the formula NH<sub>3−<var>x</var></sub>R<sub><var>x</var></sub> where R = alkyl or [[aryl]]. Related to these are pyridine and its derivatives.
*[[phosphine]]s of the formula PR<sub>3−<var>x</var></sub>Ar<sub><var>x</var></sub>.
*compounds of O, S, Se and Te in oxidation state −2, including water, [[ether]]s, [[ketone]]s

The most common Lewis bases are anions. The strength of Lewis basicity correlates with the {{var|pK<sub>a</sub>}} of the parent acid: acids with high {{var|pK<sub>a</sub>}}'s give good Lewis bases. As usual, a [[Acid strength|weaker acid]] has a stronger [[conjugate base]].

* Examples of Lewis bases based on the general definition of electron pair donor include:
**simple anions, such as [[hydride|H<sup>−</sup>]] and [[fluoride|F<sup>−</sup>]]
**other lone-pair-containing species, such as H<sub>2</sub>O, NH<sub>3</sub>, [[hydroxide|HO<sup>−</sup>]], and CH<sub>3</sub><sup>−</sup>
**complex anions, such as [[sulfate]]
**electron-rich {{pi}}-system Lewis bases, such as [[ethyne]], [[ethene]], and [[benzene]]

The strength of Lewis bases have been evaluated for various Lewis acids, such as I<sub>2</sub>, SbCl<sub>5</sub>, and BF<sub>3</sub>.<ref>Christian Laurence and Jean-François Gal "Lewis Basicity and Affinity Scales : Data and Measurement"
Wiley, 2009. {{ISBN|978-0-470-74957-9}}.{{page needed|date=September 2021}}</ref>
{| class="wikitable collapsible" align="center" border="1" cellspacing="0" cellpadding="0" style="margin: 0 0 0 0em; background: #FFFFFF; border-collapse: collapse; border-color: #C0C030;"
|+ style="background:#ffdead;"| Heats of binding of various bases to [[Boron trifluoride|BF<sub>3</sub>]]
|-
! style="background:#ffdead;"| Lewis base
! style="background:#ffdead;"| Donor atom
! style="background:#ffdead;"| Enthalpy of complexation (kJ/mol)
|-
|[[Quinuclidine]]
|N
|150
|-
|[[Triethylamine|Et<sub>3</sub>N]]
|N
|135
|-
|[[Pyridine]]
|N
|128
|-
|[[Acetonitrile]]
|N
|60
|-
|[[Dimethylacetamide|DMA]]
|O
|112
|-
|[[Dimethyl sulfoxide|DMSO]]
|O
|105
|-
|[[THF]]
|O
|90.4
|-
|[[Diethylether|Et<sub>2</sub>O]]
|O
|78.8
|-
|[[Acetone]]
|O
|76.0
|-
|[[Ethylacetate|EtOAc]]
|O
|75.5
|-
|[[Trimethylphosphine]]
|P
|97.3
|-
|[[Tetrahydrothiophene]]
|S
|51.6
|-
|}

===Applications of Lewis bases===
{{main|Homogeneous catalysis}}
Nearly all electron pair donors that form compounds by binding transition elements can be viewed [[ligand]]s. Thus, a large application of Lewis bases is to modify the activity and selectivity of [[homogeneous catalysis|metal catalysts]]. Chiral Lewis bases, generally [[multidentate]], confer [[chirality (chemistry)|chirality]] on a catalyst, enabling [[asymmetric catalysis]], which is useful for the production of [[pharmaceutical]]s.  The industrial synthesis of the anti-hypertension drug [[mibefradil]] uses a chiral Lewis base (''R''-MeOBIPHEP), for example.<ref name="CompAsymmetricCatalysis">{{cite book
 |title=Comprehensive Asymmetric Catalysis
 |editor1-last=Jacobsen |editor1-first=E.N. 
 |editor2-last=Pfaltz |editor2-first=Andreas 
 |editor3-last=Yamamato |editor3-first=H. 
 |year=1999
 |publisher=Springer
 |location=Berlin; New York
 |isbn=978-3-540-64336-4
 |pages=1443–1445
}}</ref>
[[File:Partial Roche Synthesis of Mibefradil.tif|center|700px]]
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