Lewis Acid/Base Interaction Matrix Database

Lobe-LUMO Lewis Acids

Vacant p-Orbital Species

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

FMO Topology: Lobe-LUMO Lewis acid species either have a vacant p orbital (R3C+ or F3B), or they have an important resonance structure (ie a 'mixed-in' LUMO) which gives the species considerable vacant p orbital character. Such Lobe-LUMO centres are polarised delta+.
Charge: Positive or delta+.
HSAB:

Hard to soft. Hardness of Lobe-LUMO Lewis acids is here defined with respect to the carbon-hydrogen bond length in methane (109pm).

All Lobe-LUMO Lewis acids can complex with hydride ion and the corresponding Type 11 Complex's Lewis acid to hydride bond length serves to probe the Lewis acid's chemistry.

It transpires that bond-length data is linear along congeneric series and over planars. It is convenient to nominate methane as a reference Lobe-LUMO Lewis acid because of its importance in organic chemistry.

Methane can be deconstructed to the carbenium ion Lobe-LUMO Lewis acid and a Hydride ion Lewis base. The H3C+-to-H bond length, ie methane's C-H bond length of 109pm, can be used as a reference point with which to compare to other Lobe-LUMO Lewis acids.

Congeneric species with 'Lewis acid-to-H' bond lengths shorter than 109pm (such as the hydroxy cation HO+, HOH bond length = 96pm) are deemed to be harder than the carbenium ion.

Many Lobe-LUMO Lewis acids react via concerted SN2 mechanisms. These reactions exhibit transition state symbiosis. Hard nucleofuges, such as fluorosulfonate FSO2O, render the Lobe-LUMO centre harder, and soft nucleofuges, such as iodide ion I, render the centre softer.

Chemistry:

Species are susceptible to attack by nucleophilic Lewis bases and they may be actively electrophilic. Lobe-LUMO Lewis acids increase the extent of the sigma-skeleton when they complex with nucleophiles.

There are three subclasses of Lobe-LUMO Lewis acids. Members of each subclass have the property that they complex with, or are attacked by, nucleophilic Lewis bases.

Vacant p-orbital Lewis Acids
Trivalent boron and aluminium species, BF3 and AlCl3, and enium ions of the type R3C+, RO+, Br+. The methyl cation carbenium ion, H3C+, is a useful reference species.

Species undergo A + B -> A-B complexation reactions, where B is a nucleophile, Nu:

There are several congeneric series:

And many congeneric dots:

R-Nfg Complexes
Where Nfg = nucleofuge or Lewis base leaving group.

Species susceptible to SN1 and SN2 nucleophilic substitution: H3C-I, (H3C)3C-Cl, H3C-OTs, epoxides etc.

The (usually carbon) centre attached to the nucleofuge is rendered delta+:

Alkyl groups stabilise the carbenium ion centre:

There quite a number of nucleofugal leaving groups, including halide ions, sulfate, tosylate, triflate, etc.

The liability of a leaving group – how easily it is displaced – correlates with the pKa of Lewis base's conjugate acid. Thus, an Nfg with a strong conjugate Brønsted acid, such as bromide ion (HBr) is a good leaving group and is easily displaced.

Further examples are found with three membered rings with an O, N, S, etc. heteroatom, and that are susceptible to nucleophilic attack and ring opening:

π-Heteroatom Functions
Polarised π-bonded functional groups susceptible to nucleophilic addition, or nucleophilic addition-followed-by-elimination, which leads to net substitution.

The delta+ carbon centres of imines, carbonyls, alpha,beta-unsaturated carbonyls, etc.:

 

Congeneric Series A rich source of congeneric series.
Lobe-LUMO Lewis acid (generic)
Acetate ester (generic)

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Acetonitrile, protonated

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Acetyl cation

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Acid chloride (generic)

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Acyl cation (generic)

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Acyl cation synthon (generic)

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Aldehyde (generic)

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Aldehyde, alpha-hydrogen (generic)

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Aldehyde, protonated (generic)

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Alkoxy cation (generic)

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Alkyl alkoxy hydroxy carbenium ion (generic)

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Alkyl bromide (generic)

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1° Alkyl bromide (generic)

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2° Alkyl bromide (generic)

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Alkyl chloride (generic)

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2° Alkyl chloride (generic)

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2° Alkyl iodide (generic)

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Alkyl methyl carbenium ion (generic)

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Alkyl-Nfg complex (generic)

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1° Alkyl-Nfg complex (generic)

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3° Alkyl-Nfg complex (generic)

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2° Alkyl-Nfg complex (generic)

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Allylic cation synthon (generic)

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Aluminium bromide

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Aluminium chloride

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Aluminium chloride dimer

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Aluminium fluoride

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Aluminium hydride

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Aluminium iodide

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1° Amide (generic)

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2° Amide (generic)

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3° Amide (generic)

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Amide, protonated (generic)

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Anhydride (generic)

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Antimony(III) chloride

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Antimony(III) fluoride

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Antimony(v) chloride

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Arenium ion (generic)

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Azide (generic)

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Benzoyl cation

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Benzyl bromide

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Benzyl cation

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Benzyl cation (generic)

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Benzyl-Nfg complex (generic)

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Beryllium hydroxide

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Borane

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Boron tribromide

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Boron trichloride

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Boron trifluoride

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Boron triiodide

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Brønsted acid, oxonium (generic)

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Bromine

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Bromine cation

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Bromine chloride

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alpha-Bromo ketone (generic)

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alpha-Bromoaldehyde (generic)

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Bromohydrin (generic)

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alpha-Bromomethyl ketone (generic)

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tertiary Butyl carbocation

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Carbene, alkyl (generic)

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Carbene, dialkyl (generic)

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Carbenium ion

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Carbenium ion (generic)

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Carbenium ion, alkoxy (generic)

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Carbenium ion, alkyl (generic)

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Carbenium ion, beta-amino (generic)

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Carbenium ion, beta-ether (generic)

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Carbenium ion, beta-thioether (generic)

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Carbenium ion, dialkoxy (generic)

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Carbenium ion, dialkyl (generic)

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Carbenium ion, trialkyl (generic)

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Carboiimide (generic)

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Carbon dioxide

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Carbonate diester (generic)

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Carbonyl function (generic)

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Carboxylic acid, protonated (generic)

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Chlorine

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Chlorine cation

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beta-Chloroethyl amine (generic)

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beta-Chloroethyl ether (generic)

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beta-Chloroethyl thioether (generic)

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Chlorohydrin (generic)

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Chlorosulfonic acid

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Cumulene (generic)

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Cyanogen bromide

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Cyanogen chloride

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Cyanogen iodide

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Cyanohydrin, alkyl (generic)

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alpha-Cyclopropyl cation

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Cyclopropyl, methyl cation synthon (generic)

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Dialkylhydroxy carbenium ion (generic)

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Diazomethane

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Dichlorocarbene

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Dicyclohexylcarbodiimide

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Diethyl aluminium cyanide

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Dihydroxymethyl carbenium ion

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Diidomethane

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Diisobutylaluminium hydride

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Dimethylethylcarbenium ion

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Dimethylformamide, protonated

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Dimethylhydroxy carbenium ion

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Dioxygen cation

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Diphenyl carbenium ion

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Disulfide, organic (generic)

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Enone (generic)

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Epoxide (generic)

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Ester (generic)

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Ethenyl bromonium ion

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Ethylcarbenium ion

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Ethylene oxide

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Ethylene sulfide

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Ethylium ion

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Fluorine cation

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Formaldehyde

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Formate ester (generic)

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Formyl cation

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Formyl chloride

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Gallium bromide

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Gallium chloride

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Gallium fluoride

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Gallium hydride

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Gallium iodide

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gem-Dichloride (generic)

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Hydrogen sulfenium ion

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beta-Hydroxy aldehyde (generic)

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Hydroxy carbenium ion

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Hydroxy cation

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Hydroxydialkoxy carbenium ion (generic)

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Hydroxymethyl carbenium ion

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Indium chloride

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Indium fluoride

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Indium hydride

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Indium iodide

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Indium(III) bromide

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Iodide, organic (generic)

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Iodine

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Iodine azide

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Iodine cation

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Iodine cyanate

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Iodine monobromide

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Iodine monochloride

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Iodine monofluoride

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Isocyanate (generic)

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Isothiocyanate (generic)

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alpha-Keto carbenium ion (generic)

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alpha-Keto carbenium synthon (generic)

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beta-Ketoester (generic)

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Ketone (generic)

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Ketone, alkyl phenyl (generic)

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Ketone, gamma-alkyl (generic)

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Malonate diester (generic)

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Methyl ester (generic)

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Methyl formate

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Methyl iodide

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Methyl ketone (generic)

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alpha-Methyl ketone (generic)

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Methyl-Nfg complex (generic)

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Methylene

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N5 Cation

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Neopentyl cation

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Nitrene (generic)

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Nitrenium ion

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Nitrile (generic)

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Nitrilium ion (generic)

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Nitronium ion

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Nitrosonium ion

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Nitrosyl chloride

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Orthoboric acid

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Oxime (generic)

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Peroxide, organic (generic)

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Phenyl cation

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Phenyl ester (generic)

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Phenyl selenenyl bromide

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Phenyl selenium cation

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Phosgene

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Phosphorus oxychloride

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Phosphorus pentachloride

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Phosphorus trichloride

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Propargylic cation

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Propargylic cation synthon (generic)

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beta-Propiolactone

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Selenium cation (generic)

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Silyl cation (generic)

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Sulfonylchloride (generic)

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Sulfoxide (generic)

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Sulfur dioxide

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1,1,2,2- Tetrachloroalkane (generic)

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Thallium(I) bromide

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Thallium(I) fluoride

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Thallium(III) bromide

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Thallium(III) chloride

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Thallium(III) fluoride

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Thiocarbenium ion (generic)

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Thiocation (generic)

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Thiocyanate (generic)

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Thioketone (generic)

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Thionyl chloride

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Thiourea

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p-Toluenesulfonylchloride

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Trialkylborane (RCH2CH2)3B (generic)

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Trialkylsulfonium ion (generic)

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Triethylaluminium

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Triethylborane

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Trimethyl borate

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Trimethylaluminium

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Trimethylborane

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Trimethyloxonium ion

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Trimethylsilyl cation

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Triphenylmethyl carbenium ion

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alpha, beta-Unsaturated EWG function (generic)

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Urea

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Urea or carbonate (generic)

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Urea, protonated

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Vinyl chloride (generic)

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Vinyl ether (generic)

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Zeolite

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Poster
Nucleophiles & Bases

© Mark R. Leach 1999-


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