Periodic Table
T-Shirts & more
from the
meta-synthesis



Merch Store


previous home next

Lewis Acid/Base Interaction Matrix Database


π-LUMO Lewis Acids

π-LUMO Lewis Acids

If an extended electron poor π-system species reacts via a single atomic centre, for example when a benzyl cation is reduced to toluene, the species is better considered behaving as an ambidentate, π-stabilised Lobe-LUMO Lewis acid.

However, when when the species reacts via its extended π-system directly, for example during Diels-Alder cycloaddition or when forming a π-organometallic, the the species should be considered as a π-HOMO Lewis base species. Thus, there is an overlap between π-stabilised Lobe-LUMO and π-LUMO classification.

Search for π-LUMO Lewis acid species in The Chemical Thesaurus

FMO Topology:

Delocalised cationic hydrocarbon π-systems and those neutral but electron deficient π-functions which participate in concerted multicentre reactions.

Hückel MO theory gives rise to whole families of π-structure: polyene ribbons, aromatics, etc. Each system is FMO unique. π-Species must be considered at the Hückel level, as well as by VB resonance techniques.

Indeed, quantum mechanics is all about patterns. A particularly striking manifestation is seen with the polyene system of: 1, 2, 3, 4, 5, 6... conjugated p-orbital systems and how they give rise to the cabenium ion, allyl cation & pentatrieneyl cation and alkene, 1,3-diene & 1,3,5-triene π-LUMO Lewis acids:

Charge: Positive or δ+ electron poor π-systems.
HSAB: Intrinsically soft.
Chemistry:

Species behave as π-LUMO Lewis acid species when they undergo FMO controlled multicentre interactions. These most obviously manifest themselves in three situations:

  • Stabilisation of the π-system: certain patterns/structures are associated with stability such as 4n+2 π-electrons in a cyclic array, the allyl cation, etc.

  • Diels-Alder cycloaddition and other pericyclic interactions, Type 20 Lewis acid/base complexation.

  • Having non-nucleophilic complex anion Lewis base anions to stabilise the π-LUMO Lewis acid species.
Congeneric Series:

Few congeneric series, but the chloronitrobenzene series can be considered congeneric with respect to the nucleophilic displacement of Cl by a nucleophile:

pi-LUMO Lewis acid (generic)
Acrylonitrile

more here
Alkene LUMO (generic)

more here
Allyl cation

more here
Allyl cation (generic)

more here
Arenium ion (generic)

more here
Aronium ion (generic)

more here
Azoniaanthracene ion

more here
Azulene

more here
Benzaldehyde

more here
Benzaldehyde radical cation

more here
Benzene diazonium ion

more here
Benzonium ion

more here
Benzyl cation

more here
Benzyl cation (generic)

more here
1,3-Butadiene, s-cis

more here
1,3-Butadiene, s-trans

more here
1,3-Cyclohexadiene

more here
((1-Cyclohexenyl)methylidene)propanedinitrile

more here
Cyclopentadiene

more here
alpha-Cyclopropyl cation

more here
Diazonium ion (generic)

more here
trans 1,2-Dichloroalkene (generic)

more here
Dimethylethylcarbenium ion

more here
Diphenyl carbenium ion

more here
Enone (generic)

more here
Furan

more here
6 Heterocycle (generic)

more here
Heterocycle, polycyclic (generic)

more here
1,3,5-Hexatriene

more here
N5 Cation

more here
1,3,5,7-Octatetrene

more here
Pentadienyl cation

more here
Phenyl cation

more here
Picric acid

more here
Polyene (generic)

more here
Propargylic cation

more here
Propargylic cation (generic)

more here
Pyrrole

more here
Pyrylium ion

more here
Quinolizinium ion

more here
7,7,8,8,- Tetracyano-p-quinodimethane

more here
Tetracyanoethylene

more here
Thiophene

more here
Thiopyrylium ion

more here
Triethyloxonium tetrafluoroborate

more here
1,3,5-Trinitrobenzene

more here
Triphenylmethyl carbenium ion

more here
Tropylium ion

more here
alpha, beta-Unsaturated EWG function (generic)

more here
Vinyl chloride (generic)

more here


previous home next
Poster Nucleophiles & Bases

© Mark R. Leach 1999 –


Queries, Suggestions, Bugs, Errors, Typos...

If you have any:

Queries
Comments
Suggestions
Suggestions for links
Bug, typo or grammatical error reports about this page,

please contact Mark R. Leach, the author, using mark@meta-synthesis.com

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