Periodic Table |
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Lewis Acid/Base Interaction Matrix Database
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Onium Ion Lewis Acids

Hypervalent Molecular Cations | ![]() Search for onium ion Lewis acid species in The Chemical Thesaurus |
FMO Topology: |
The onium ion Lewis acids have a central electronegative atom saturated with Lewis acid "ligands", usually H+ or alkyl+. Onium ion Lewis acids are all proton/X Lobe-HOMO or carbenium ion/X Lobe-HOMO complexes where: X = N, O, F, Ne, P, S, Cl, Ar, As, Se, Br, Kr, Sb, Te, I, Xe |
Charge: | Positive |
HSAB: | Intrinsically hard, but species behave as a source of hard H+ or the relatively soft Lobe-LUMO Lewis acid carbenium ion, H3C+. |
Chemistry: |
Onium ions either form charge-controlled (ionic) complexes or they react by transferring a ligand to a nucleophilic /basic Lewis base. If the transferred ligand is H+, the onium ion acts as a Brønsted Acid. If the transferred ligand is a carbenium ion Lewis acid, the onium ion is said to be an alkylating agent. High symmetry tetraalkyl ammonium ions, such as [(CH3)4N]+, can act as spectator cations. Methane can be protonated to the five valent carbonium ion: [CH5]+ Second order nucleophilic substitution reactions at carbon pass through a five valent carbonium ion transition state: ![]() |
Congeneric Series: |
There is one onium ion Lewis acid planar: ![]() Ammonium, phosphonium, oxonium and sulfonium ions give rise to many ligand replacement congeneric series, for example: ![]() [R4N]+ [R3NR']+ [R2NR2]+ [RNR'3]+ [NR'4]+ where R and/or R' = H, CH3, alkyl, C6H5 etc. |
Onium ion Lewis acid (generic)![]() |
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Aldehyde, protonated (generic) more here |
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Alkyl alkoxy hydroxy carbenium ion (generic) more here |
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Alkyl oxonium ion (generic) more here |
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1° Alkyl oxonium ion (generic) more here |
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Alkyl telluronium ion (generic) more here |
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Amide, protonated (generic) more here |
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Ammonium ion more here |
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1° Ammonium ion (generic) more here |
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2° Ammonium ion (generic) more here |
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3° Ammonium ion (generic) more here |
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4° Ammonium ion (generic) more here |
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Aqueous mineral acid, 0.05 to 1.0 molar (generic) more here |
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Argonium ion more here |
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Aronium ion (generic) more here |
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Arsonium ion more here |
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Arsonium ion (generic) more here |
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Benzene diazonium ion more here |
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Benzonium ion more here |
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Brønsted acid, oxonium (generic) more here |
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Bromonium ion more here |
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tertiary Butyl oxonium ion 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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Carbonium ion more here |
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Carboxylic acid, protonated (generic) more here |
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Chloronium ion more here |
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Chloronium ion, alkyl (generic) more here |
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Dialkyl oxonium ion (generic) more here |
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Dialkyl telluronium ion (generic) more here |
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Dialkylhydroxy carbenium ion (generic) more here |
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Diazonium ion (generic) more here |
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Difluorochloronium ion more here |
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Dihydroxymethyl carbenium ion more here |
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Dimethyl sulfonium ion more here |
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Dimethylammonium ion more here |
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Dimethylformamide, protonated more here |
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Dimethylhydroxy carbenium ion more here |
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Dimethyloxonium ion more here |
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Dimethylsulfoxide, protonated more here |
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Diphenylammonium ion more here |
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Duteronium ion more here |
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Eigen Cation more here |
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Ethenyl bromonium ion more here |
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Ethylacetate, protonated more here |
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Ethylbenzene SeAr intermediate more here |
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Fluoronium ion more here |
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Fluoronium ion, alkyl (generic) more here |
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Guanidine, protonated more here |
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Hydrazinium ion more here |
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Hydronium ion, [H3]+ more here |
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Hydroxy acid, protonated (generic) more here |
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Hydroxy carbenium ion more here |
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Hydroxyammonium ion 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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Imidazonium ion more here |
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Iodonium ion more here |
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Iodonium ion, alkyl (generic) more here |
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Isopropyl oxonium ion more here |
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Kryptonium ion more here |
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Methylammonium ion more here |
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Methyloxonium ion more here |
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Methylsulfonium ion more here |
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Methyltriethylammonium ion more here |
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Neonium ion more here |
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Nitric acid, protonated more here |
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Nitrilium ion (generic) more here |
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Nitrobenzene SeAr intermediate more here |
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Nitrobenzene, protonated more here |
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Nitromethane, protonated more here |
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Oxonium ion more here |
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Phenyl ammonium ion (generic) more here |
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Phenylammonium ion more here |
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Phenylethanone SeAr intermediate more here |
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Phenyloxonium ion more here |
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Phosphonium ion more here |
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Phosphonium ion (generic) more here |
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Phosphonium ion, alkyl triphenyl (generic) more here |
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Protonated base, [H-B]+ (generic) more here |
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Pyridinium ion more here |
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Pyrylium ion more here |
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Selenonium ion more here |
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Stibonium ion more here |
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Sulfonium ion more here |
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Sulfonium ion, alkyl (generic) more here |
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Sulfonium ion, dialkyl (generic) more here |
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Telluronium ion more here |
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Tetrahydrofuran, protonated more here |
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Tetramethylammonium ion more here |
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Thiocarbenium ion (generic) more here |
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Thiopyrylium ion more here |
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Trialkyloxonium ion (generic) more here |
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Trialkylsulfonium ion (generic) more here |
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Triethylarsonium ion more here |
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Trimethylammonium ion more here |
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Trimethyloxonium ion more here |
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Trimethylphosphonium ion more here |
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Trimethylsulfonium ion more here |
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Trimethylsulfoxonium iodide more here |
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Trimethylsulfoxonium ion more here |
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Triphenyloxonium ion more here |
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Urea, protonated more here |
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Xenon fluoride cation more here |
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Xenon, protonated more here |
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Ylid (generic) more here |
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Zundel cation more here |
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Poster | Nucleophiles & Bases |
© Mark R. Leach 1999 –
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