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The Chemogenesis Analysis: An Overview

Abstract... What It's All About... In a Nutshell... Executive Summary... Chemogenesis in 700 Seconds... Chemogenesis explores the nature of chemical structure and reactivity in logical steps, each described over one or two pages of this web book.

Main Group Element Hydrides

The story starts with the main group elements, as their hydrides.

This set includes many common chemicals with well known and understood properties and behaviours: hydrogen, methane, water, hydrogen bromide, argon, etc.

The Five hydrogen Probe Experiments

Five hydrogen probe experiments are performed upon the set of main group elemental hydrides:

Observations:

Note the colour scheme: Lewis acids are red, Lewis bases are blue & radicals are green which will be used consistantly throughout this web book.

Congeneric Array Interactions

Concentrating on the Lewis acid and Lewis base arrays:

Several pages chemogenesis web book are spent exploring how linear structural and reactivity traits can be found with respect to atomic ionic radii, bond length, electronegativity, % ionic bond character and pKa.

FMO Theory

At this point we introduce some simple frontier molecular orbital (FMO) theory: Theory, diatomics, polyatomics & π-systems.

FMO theory identifies that reactive chemical species interact with each other via a rather limited set of frontier molecular orbitals, the FMOs:

Collecting It All Together...

It is found that there are five general types of reactive species and associated electronic chemical reactivity behaviour:

Types of Lewis acid and Lewis base

The next step is to take the arrays of Lewis acid and Lewis base species generated by five hydrogen probe experiments and sort them by frontier molecular orbital type, topology (3D geometrical shape + phase information) and reactivity behaviour.

At this point we slide into the analysis three additional types of Lewis acid and Lewis base:

In toto, it transpires that there are Four general types of Lewis base and Six general types of Lewis acid:


Four General Types of Lewis Base:

  • s-HOMO Lewis bases: hydride ion, H–, and hydrogen, H2

  • Complex Anion Lewis bases: tetrafluoroborate ion, [BF4]–

  • Lobe-HOMO Lewis bases: hydroxide ion, HO–, water, H2O:, methylcarbanion, H3C–, etc.

  • π-System Lewis bases electron rich π-systems: ethene, benzene, etc.

Six General Types of Lewis acid:

  • The Proton Lewis acid: the proton, H+

  • s-LUMO Lewis acids: Group 1 and 2 cations: Li+, Mg2+, etc.

  • Onium Ion Lewis acids: ammonium ion, [NH4]+, oxonium ion, [OH3]+, etc.

  • Lobe-LUMO Lewis acids: boron trifluoride, BF3, the carbenium ion, H3C+

  • π-LUMO Lewis acids: electron poor π-systems, enones, tetracyanoethylene, etc.

  • Heavy Metal Lewis acids: cations, bulk metals of the transition metals, post-transition metals, lanthanides & actinides

Congeneric arrays are always found within a Lewis acid or Lewis base type, but never crossing types.

The Lewis Acid/Base Interaction Matrix

Each of the four types of Lewis base and six types of Lewis acid exhibits distinct electronic structure and characteristic reaction chemistry behaviour. It follows that the four types of Lewis bases interact with the six types of Lewis acid to produce a matrix of Lewis acid/base complexes.

Crucially, each and every cell of the Lewis acid/base interaction matrix encapsulates and exhibits distinct electronic structure and characteristic reaction chemistry behaviour:

For example, an s-LUMO Lewis acid such as the sodium ion, Na+, interacts with a Lobe-HOMO Lewis bases such as the hydroxide ion, HO–, to give sodium hydroxide, a Type 7 Lewis acid/base complex.

The point is that most of the basic, proton abstracting reagents and many of the neutral inorganic salts used in the chemistry laboratory are Type 7 Lewis acid/base complexes, including:

methyl lithium, LiCH3
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

Like the periodic table, the Lewis acid/base interaction matrix is a schema and an extraordinary object with many properties. For example, the vast majority of the reaction chemistry taught to school and university students can be mapped to the Lewis acid/base interaction matrix with the effect that the chemistry has context, rather than existing as isolated facts.

Each cell of the matrix is discussed in detail, and each cell represents distinct chemistry:



Prof. Roald Hoffmann, who won the Nobel prize for his work FMO theory, wrote in a personal communication:

"A great combination of frontier orbital (of course I like that) and chemical ways. I like it."

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Classification of Matter Lewis & Brønsted Models of Acidity

© Mark R. Leach 1999 –

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This free, open access web book is an ongoing project and your input is appreciated.