Periodic Table |
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Lewis Acid/Base Interaction Matrix Database
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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 δ+. |
Charge: | Positive or δ+. |
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 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 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 δ+: ![]() 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 The δ+ carbon centres of imines, carbonyls, alpha,beta-unsaturated carbonyls, etc.: ![]() ![]()
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Congeneric Series | A rich source of congeneric series. |
Lobe-LUMO Lewis acid (generic)![]() |
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Acetate ester (generic) more here |
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Acetonitrile, protonated more here |
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Acetyl cation more here |
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Acid chloride (generic) more here |
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Acyl cation (generic) more here |
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Acyl cation synthon (generic) more here |
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Aldehyde (generic) more here |
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Aldehyde, alpha-hydrogen (generic) more here |
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Aldehyde, protonated (generic) more here |
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Alkoxy cation (generic) more here |
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Alkyl alkoxy hydroxy carbenium ion (generic) more here |
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Alkyl bromide (generic) more here |
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1° Alkyl bromide (generic) more here |
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2° Alkyl bromide (generic) more here |
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Alkyl chloride (generic) more here |
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2° Alkyl chloride (generic) more here |
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2° Alkyl iodide (generic) more here |
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Alkyl methyl carbenium ion (generic) more here |
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Alkyl-Nfg complex (generic) more here |
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1° Alkyl-Nfg complex (generic) more here |
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3° Alkyl-Nfg complex (generic) more here |
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2° Alkyl-Nfg complex (generic) more here |
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Allylic cation synthon (generic) more here |
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Aluminium bromide more here |
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Aluminium chloride more here |
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Aluminium chloride dimer more here |
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Aluminium fluoride more here |
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Aluminium hydride more here |
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Aluminium iodide more here |
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1° Amide (generic) more here |
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2° Amide (generic) more here |
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3° Amide (generic) more here |
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Amide, protonated (generic) more here |
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Anhydride (generic) more here |
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Antimony(III) chloride more here |
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Antimony(III) fluoride more here |
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Antimony(v) chloride more here |
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Arenium ion (generic) more here |
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Azide (generic) more here |
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Benzoyl cation more here |
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Benzyl bromide more here |
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Benzyl cation more here |
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Benzyl cation (generic) more here |
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Benzyl-Nfg complex (generic) more here |
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Beryllium hydroxide more here |
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Borane more here |
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Boron tribromide more here |
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Boron trichloride more here |
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Boron trifluoride more here |
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Boron triiodide more here |
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Brønsted acid, oxonium (generic) more here |
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Bromine more here |
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Bromine cation more here |
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Bromine chloride more here |
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alpha-Bromo ketone (generic) more here |
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alpha-Bromoaldehyde (generic) more here |
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Bromohydrin (generic) more here |
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alpha-Bromomethyl ketone (generic) more here |
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tertiary Butyl carbocation more here |
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Carbene, alkyl (generic) more here |
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Carbene, dialkyl (generic) more here |
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Carbenium ion more here |
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Carbenium ion (generic) more here |
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Carbenium ion, alkoxy (generic) more here |
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Carbenium ion, alkyl (generic) more here |
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Carbenium ion, beta-amino (generic) more here |
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Carbenium ion, beta-ether (generic) more here |
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Carbenium ion, beta-thioether (generic) more here |
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Carbenium ion, dialkoxy (generic) more here |
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Carbenium ion, dialkyl (generic) more here |
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Carbenium ion, trialkyl (generic) more here |
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Carboiimide (generic) more here |
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Carbon dioxide more here |
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Carbonate diester (generic) more here |
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Carbonyl function (generic) more here |
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Carboxylic acid, protonated (generic) more here |
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Chlorine more here |
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Chlorine cation more here |
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beta-Chloroethyl amine (generic) more here |
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beta-Chloroethyl ether (generic) more here |
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beta-Chloroethyl thioether (generic) more here |
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Chlorohydrin (generic) more here |
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Chlorosulfonic acid more here |
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Cumulene (generic) more here |
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Cyanogen bromide more here |
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Cyanogen chloride more here |
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Cyanogen iodide more here |
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Cyanohydrin, alkyl (generic) more here |
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alpha-Cyclopropyl cation more here |
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Cyclopropyl, methyl cation synthon (generic) more here |
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Dialkylhydroxy carbenium ion (generic) more here |
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Diazomethane more here |
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Dichlorocarbene more here |
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Dicyclohexylcarbodiimide more here |
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Diethyl aluminium cyanide more here |
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Dihydroxymethyl carbenium ion more here |
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Diidomethane more here |
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Diisobutylaluminium hydride more here |
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Dimethylethylcarbenium ion more here |
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Dimethylformamide, protonated more here |
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Dimethylhydroxy carbenium ion more here |
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Dioxygen cation more here |
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Diphenyl carbenium ion more here |
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Disulfide, organic (generic) more here |
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Enone (generic) more here |
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Epoxide (generic) more here |
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Ester (generic) more here |
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Ethenyl bromonium ion more here |
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Ethylcarbenium ion more here |
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Ethylene oxide more here |
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Ethylene sulfide more here |
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Ethylium ion more here |
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Fluorine cation more here |
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Formaldehyde more here |
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Formate ester (generic) more here |
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Formyl cation more here |
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Formyl chloride more here |
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Gallium bromide more here |
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Gallium chloride more here |
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Gallium fluoride more here |
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Gallium hydride more here |
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Gallium iodide more here |
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gem-Dichloride (generic) more here |
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Hydrogen sulfenium ion more here |
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beta-Hydroxy aldehyde (generic) more here |
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Hydroxy carbenium ion more here |
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Hydroxy cation more here |
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Hydroxydialkoxy carbenium ion (generic) more here |
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Hydroxymethyl carbenium ion more here |
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Indium chloride more here |
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Indium fluoride more here |
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Indium hydride more here |
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Indium iodide more here |
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Indium(III) bromide more here |
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Iodide, organic (generic) more here |
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Iodine more here |
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Iodine azide more here |
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Iodine cation more here |
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Iodine cyanate more here |
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Iodine monobromide more here |
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Iodine monochloride more here |
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Iodine monofluoride more here |
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Isocyanate (generic) more here |
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Isothiocyanate (generic) more here |
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alpha-Keto carbenium ion (generic) more here |
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alpha-Keto carbenium synthon (generic) more here |
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beta-Ketoester (generic) more here |
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Ketone (generic) more here |
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Ketone, alkyl phenyl (generic) more here |
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Ketone, gamma-alkyl (generic) more here |
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Malonate diester (generic) more here |
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Methyl ester (generic) more here |
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Methyl formate more here |
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Methyl iodide more here |
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Methyl ketone (generic) more here |
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alpha-Methyl ketone (generic) more here |
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Methyl-Nfg complex (generic) more here |
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Methylene more here |
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N5 Cation more here |
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Neopentyl cation more here |
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Nitrene (generic) more here |
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Nitrenium ion more here |
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Nitrile (generic) more here |
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Nitrilium ion (generic) more here |
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Nitronium ion more here |
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Nitrosonium ion more here |
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Nitrosyl chloride more here |
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Orthoboric acid more here |
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Oxime (generic) more here |
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Peroxide, organic (generic) more here |
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Phenyl cation more here |
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Phenyl ester (generic) more here |
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Phenyl selenenyl bromide more here |
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Phenyl selenium cation more here |
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Phosgene more here |
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Phosphorus oxychloride more here |
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Phosphorus pentachloride more here |
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Phosphorus trichloride more here |
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Propargylic cation more here |
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Propargylic cation synthon (generic) more here |
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beta-Propiolactone more here |
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Selenium cation (generic) more here |
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Silyl cation (generic) more here |
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Sulfonylchloride (generic) more here |
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Sulfoxide (generic) more here |
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Sulfur dioxide more here |
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1,1,2,2- Tetrachloroalkane (generic) more here |
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Thallium(I) bromide more here |
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Thallium(I) fluoride more here |
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Thallium(III) bromide more here |
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Thallium(III) chloride more here |
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Thallium(III) fluoride more here |
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Thiocarbenium ion (generic) more here |
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Thiocation (generic) more here |
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Thiocyanate (generic) more here |
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Thioketone (generic) more here |
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Thionyl chloride more here |
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Thiourea more here |
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p-Toluenesulfonylchloride more here |
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Trialkylborane (RCH2CH2)3B (generic) more here |
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Trialkylsulfonium ion (generic) more here |
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Triethylaluminium more here |
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Triethylborane more here |
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Trimethyl borate more here |
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Trimethylaluminium more here |
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Trimethylborane more here |
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Trimethyloxonium ion more here |
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Trimethylsilyl cation more here |
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Triphenylmethyl carbenium ion more here |
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alpha, beta-Unsaturated EWG function (generic) more here |
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Urea more here |
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Urea or carbonate (generic) more here |
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Urea, protonated more here |
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Vinyl chloride (generic) more here |
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Vinyl ether (generic) more here |
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Zeolite more here |
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Poster | Nucleophiles & Bases |
© Mark R. Leach 1999 –
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