School and university students learn that electron pair donor Lewis bases "react with" or "complex with" or "interact with" electron pair acceptor Lewis acids. The previous page showed that there are six quite distinct types of Lewis acid and four quite distinct types types of Lewis base, where distinction is by frontier molecular orbital (FMO) topology. It follows that the the six types of Lewis acid and the four types of Lewis base inevitably interact to give 24 distinct types of Lewis acid/base complex. The range of chemistry encompassed and described by the Lewis Acid/Base Interaction Matrix is quite staggering; it ranges across organic, inorganic and organometallic reaction chemistry in such a way that each is seen as an inevitable manifestation of main group chemistry. The Lewis acid/base interaction matrix is the core finding of the chemogenesis analysis.
Six Types of Lewis Acid and Four Types of Lewis Base
The previous page introduced the notion that there are four distinct types of Lewis base, where classification is based on the frontier molecular orbital FMO topology. These four types of Lewis base are:
s-HOMO Lewis bases: H–, H2
Complex Anion Lewis bases: [BF4]–, [SbF6]–, etc.
Lobe-HOMO Lewis bases: HO–, H2O:, etc.
p-HOMO Lewis bases: allyl anion, ethene, etc.
The previous page also introduced the notion that there are six distinct types of Lewis acid, again where classification is based on FMO topology. These six types of Lewis acid are:
The Proton Lewis acid, H+
s-LUMO Lewis acids, Na+, Mg2+, etc.
Onium Ion Lewis Acids: [NH4]+, [(Me3)3O]+, etc.
Lobe-LUMO Lewis Acids: BF3, R3C+, etc.
p-LUMO Lewis Acids: allyl cation, etc.
Heavy Metal Lewis Acids: metals & cations, etc.
Lewis Acid/Base Complexes
Lewis acid/base interaction chemistry can be stated in two ways:
- Electron pair donor Lewis bases "react with" or "complex with" or "interact with" electron pair acceptor Lewis acids to give Lewis acid/base complexes.
- The highest occupied molecular orbital (HOMO) of a Lewis base "reacts with" or "complexes with" or "interacts with" the lowest unoccupied molecular orbital (LUMO) of a Lewis acid to give a Lewis acid base complex with a bonding molecular orbital. The contributions of +/– charge and orbital overlap is described by the Klopman equation, here.
The six distinct types of Lewis acid and the four distinct types of Lewis base – where distinction is by frontier molecular orbital (FMO) topology, ie the shape, phase and geometry of the participating HOMOs and LUMOs – interact to give 24 distinct types of Lewis acid/base complex. This process can be visualised with the aid of the Lewis acid/base interaction matrix graphic:
The Lewis acid/base interaction matrix – or interaction table, a type of Karnaugh map – has many, many properties. For example:
• Each cell of the Lewis acid/base interaction matrix contains distinct and characteristic chemistry.
• The matrix covers all Lewis acid/base reaction chemistry space.
We shall explore this object in some detail.
Across and Up-Down
The characteristic chemistry of a particular type of Lewis acid can be found by reading across the interaction matrix. Likewise, read up/down down for a particular type of Lewis base:
For example, an s-LUMO Lewis acid such as the sodium ion, Na+, interacts with Lobe-HOMO Lewis base such as the hydroxide ion, HO–, to give a Type 7 complex.
The point is that nearly all basic, proton abstracting reagents used in chemistry are also Type 7 complexes including:
methyl lithium, H3CLi
potassium hydroxide, KOH
sodium carbonate, Na2CO3
sodium hydrogen carbonate, NaHCO3
sodamide, NaNH2
lithium fluoride, LiF
calcium hydroxide, Ca(OH)2
sodium sulfide, Na2S
sodium cyanide, NaCN
magnesium oxide, MgO
barium sulfate, BaSO4
etc.
Complexation Type Numbers
Each of the interaction complex types is assigned a number from 1 to 24. These numbers are used to "keep track" and have no real significance... other than the fact that they are used in a self-consistent in this web book and The Chemical Thesaurus reaction chemistry database:
Real Species
When the schematic Lewis acid/base interaction matrix icons are replaced with real chemical species the nature and usefulness of the Lewis acid/base interaction matrix become apparent.
More Real Species
Many Lewis acid/base interactions initiate reaction mechanisms more involved than simple complexation. For example, the trimethyl oxonium ion reacts with water to give dimethyl ether and protonated methanol. This can be viewed as the transfer of a carbenium ion Lobe-LUMO Lewis acid from one Lobe-HOMO Lewis base to another. The interaction is an example of Type 11 Lewis acid/base reaction chemistry.
Lewis acid/Base Reaction Chemistries
Each of the 24 types of Lewis acid/base complexation can be mapped against well known types of reaction chemistry. For example, type 3 complexes are all "super acids" and Diels-Alder cycloaddition is associated with type 20 complexation.
Again, this logic is general in two ways:
• Firstly, each cell of the Lewis acid/base interaction matrix contains distinct and characteristic chemistry.
• Secondly, the matrix covers all of Lewis acid/base reaction chemistry space.
HSAB Analysis
In the 1960s, Ralph Pearson suggested that Lewis acids and Lewis bases should be classified as hard, borderline or soft, with the observation that: "Hard [Lewis] acids prefer to complex with hard [Lewis] bases and soft [Lewis] acids with soft [Lewis] bases", the HSAB principle (go here and here for more information).
The original HSAB analysis is very limited, but it regains its promise and power when applied after Lewis acids and Lewis bases are first classified by their frontier molecular orbital (FMO) topology. The analysis can now be used to describe the richness of bonding interactions:
Traditional Areas of Chemistry
The Patterns in Reaction Chemistry analysis makes no initial distinction between the traditional organic, inorganic and organometallic reaction chemistries (divisions cause no end of confusion to students of the subject).
Yet these historical views can be mapped onto the Lewis acid/base interaction matrix.
Searching for Congeneric Dots, Series, Planars and Volumes
Lewis acid and Lewis base types which are rich in congeneric arrays interact to give complex types which are rich in arrays.
Note, that on the diagram below there is not an exact one-to-one correspondence between the existence Lewis acid and Lewis base arrays and corresponding complex arrays. The reason is that not all complexation types are as interesting as each other. For example, Type 20 complexation is very rich... while Type 12 is not.
The rest of this page is used to explore the 24 complexation chemistries in detail.
The reader may wish to come back to this page later and fast forward to species/species interaction page, here.
Type 1 Lewis Acid/Base Complexation and Associated Reaction Chemistry
Type 2 Lewis Acid/Base Complexation and Associated Reaction Chemistry
Type 3 Lewis Acid/Base Complexation and Associated Reaction Chemistry
Type 4 Lewis Acid/Base Complexation and Associated Reaction Chemistry
Type 5 Lewis Acid/Base Complexation and Associated Reaction Chemistry
Type 6 Lewis Acid/Base Complexation and Associated Reaction Chemistry
Type 7 Lewis Acid/Base Complexation and Associated Reaction Chemistry
A congeneric volume can be found here.
Type 8 Lewis Acid/Base Complexation and Associated Reaction Chemistry
Type 9 Lewis Acid/Base Complexation and Associated Reaction Chemistry
Type 10 Lewis Acid/Base Complexation and Associated Reaction Chemistry
Type 11 Lewis Acid/Base Complexation and Associated Reaction Chemistry
Type 12 Lewis Acid/Base Complexation and Associated Reaction Chemistry
Type 13 Lewis Acid/Base Complexation and Associated Reaction Chemistry
Type 14 Lewis Acid/Base Complexation and Associated Reaction Chemistry
Type 15 Lewis Acid/Base Complexation and Associated Reaction Chemistry
Type 16 Lewis Acid/Base Complexation and Associated Reaction Chemistry
Type 17 Lewis Acid/Base Complexation and Associated Reaction Chemistry
Type 18 Lewis Acid/Base Complexation and Associated Reaction Chemistry
Type 19 Lewis Acid/Base Complexation and Associated Reaction Chemistry
Type 20 Lewis Acid/Base Complexation and Associated Reaction Chemistry
Type 21 Lewis Acid/Base Complexation and Associated Reaction Chemistry
Type 22 Lewis Acid/Base Complexation and Associated Reaction Chemistry
Type 23 Lewis Acid/Base Complexation and Associated Reaction Chemistry
Type 24 Lewis Acid/Base Complexation and Associated Reaction Chemistry
The Bridge Bond
van der Waals Attraction
Discrete molecules, such as methane, CH4, are held together internally by strong intramolecular (within molecule) "shared electron pair" covalent bonds, but when forming condensed solid or liquid phases, the molecules interact via weak intermolecular (between molecule) van der Waals forces:
- There are several types of van der Waals attraction: dipole/dipole, dipole/induced-dipole and spontaneous-dipole/induced-dipole. It is tempting to consider these forces to be of different strengths, but it is the distance range that is more important. The spontaneous-dipole/induced-dipole attractions – also known as London dispersion forces (LDF) – are surprisingly strong but only act at very short range. (It is as if the surface of even neutral, non-polar molecules like methane are 'sticky'.)
- All molecules have London dispersion forces and the strength increases with the size/surface area of the molecule. This logic is used to explains the increasing boiling and sublimation temperatures of the halogens: F2 < Cl2 < Br2 I2.
- In addition, some molecules have dipole-dipole, hydrogen bonding, etc., which increase the total amount of interaction between the molecules. Consider iodine chloride, ICl and bromine, Br2. Both are 70-electron systems, but ICl is polar and Br2 is non-polar, yet they have rather similar boiling points of 97° and 59° respectively, showing that the dipole/dipole attraction makes only a minor contribution. (Many thanks to members of the ChemEd list for the above points.)
- Molecular materials may also be hydrogen bonded, where a hydrogen bond involves a proton being shared between two Lewis bases, usually with oxygen, nitrogen or fluorine atomic centres, as discussed here.
Host/Guest Complexation
Scaling of Species
Multi-Step Reactions
Delve into a clickable version of the Lewis acid/base interaction matrix, here.
Buy a copy of Lewis Acid/Base Reaction Chemistry (book + poster + CD-ROM) here.
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PATTERNS IN REACTION CHEMISTRY The central part of the chemogenesis analysis – the identification of the five reaction chemistries, the classification of Lewis acids and Lewis bases and the formation of the Lewis acid/base interaction matrix – has been published as a poster and a book available from Meta-Synthesis.
Book is 96 page softback, the CD-ROM is Mac & PC compatible and the poster is folded. Need more information? Contact sales@meta-synthesis.com |
| Lewis Acid/Base Chemistry |
Poster
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© Mark R. Leach 1999-2008
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