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Search for onium ion Lewis acid species in The Chemical Thesaurus

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

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:

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.