Onium compounds

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Onium compounds are cations derived by the protonation of mononuclear parent hydrides of elements of the nitrogen family (Group 15), chalcogen family (Group 16), and halogen family (Group 17), and similar cations derived by the substitution of hydrogen atoms in the former by other groups, such as organic radicals, or halogens, for example tetramethylammonium, and further derivatives having polyvalent additions, such as iminium and nitrilium. (IUPAC definition[1]; other definitions vary.)

They are also known as onium ions. Compounds of these ions are known as onium salts. Onium ions have a charge of +1; double onium ions have a charge of +2, and so on.

Simple onium compounds

The following ions use a similar naming scheme, but they do not strictly meet the above definition. They are protonated hydrides of Carbon family (Group 14) elements:

The following ions use a similar naming scheme, but they do not strictly meet the above definition. They are protonated hydrides of Boron family (Group 13) elements:

The following ion uses a similar naming scheme, but it does not strictly meet the above definition. It is protonated diatomic hydrogen:

Onium compounds with monovalent substitutions

Onium compounds with polyvalent substitutions

  • quaternary ammonium cations having one double-bonded substitution, R=NH2+
  • quaternary ammonium cations having one double-bonded substitution and two single-bonded substitutions, R=NR2+
    • iminium, R2C=NR2+ (substituted protonated imine)
    • ??, RN=NR2+
  • quaternary ammonium cations having one triple-bonded substitution, R≡NH+
  • quaternary ammonium cations having one triple-bonded substitution and one single-bonded substitution, R≡NR+
  • ternary oxonium cations having one triple-bonded substitution, R≡O+
  • tertiary sulfonium cations having one triple-bonded substitution, R≡S+

Double onium compounds

External links

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