Periodic Table |
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Lewis Acid/Base Interaction Matrix Database
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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:
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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)![]() |
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Acrylonitrile more here |
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Alkene LUMO (generic) more here |
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Allyl cation more here |
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Allyl cation (generic) more here |
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Arenium ion (generic) more here |
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Aronium ion (generic) more here |
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Azoniaanthracene ion more here |
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Azulene more here |
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Benzaldehyde more here |
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Benzaldehyde radical cation more here |
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Benzene diazonium ion more here |
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Benzonium ion more here |
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Benzyl cation more here |
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Benzyl cation (generic) more here |
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1,3-Butadiene, s-cis more here |
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1,3-Butadiene, s-trans more here |
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1,3-Cyclohexadiene more here |
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((1-Cyclohexenyl)methylidene)propanedinitrile more here |
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Cyclopentadiene more here |
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alpha-Cyclopropyl cation more here |
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Diazonium ion (generic) more here |
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trans 1,2-Dichloroalkene (generic) more here |
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Dimethylethylcarbenium ion more here |
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Diphenyl carbenium ion more here |
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Enone (generic) more here |
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Furan more here |
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6 Heterocycle (generic) more here |
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Heterocycle, polycyclic (generic) more here |
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1,3,5-Hexatriene more here |
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N5 Cation more here |
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1,3,5,7-Octatetrene more here |
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Pentadienyl cation more here |
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Phenyl cation more here |
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Picric acid more here |
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Polyene (generic) more here |
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Propargylic cation more here |
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Propargylic cation (generic) more here |
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Pyrrole more here |
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Pyrylium ion more here |
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Quinolizinium ion more here |
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7,7,8,8,- Tetracyano-p-quinodimethane more here |
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Tetracyanoethylene more here |
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Thiophene more here |
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Thiopyrylium ion more here |
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Triethyloxonium tetrafluoroborate more here |
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1,3,5-Trinitrobenzene more here |
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Triphenylmethyl carbenium ion more here |
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Tropylium ion more here |
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alpha, beta-Unsaturated EWG function (generic) more here |
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Vinyl chloride (generic) more here |
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Poster | Nucleophiles & Bases |
© Mark R. Leach 1999 –
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