Arenium ion
As arenium ion (or benzenium ) is known in the organic chemistry a arene cation eg. B. protonated as C 6 H 7 + . An arenium ion is therefore a charged form of a so-called aryl. As aryl refers to a simple - or multiply-substituted benzene , suitable substituents being halogens, such as chlorine , bromine or iodine can act. Hydrogen can also contain organic radicals such as carboxy groups or other functional organochemical groupssubstitute for benzene. Particularly well-known aryls are the nitro-substituted aryls such as nitrobenzene or TNT ( trinitrotoluene ).
It is a reactive intermediate stage during the so-called electrophilic aromatic or nucleophilic substitution . The following figure shows the reaction mechanism of an electrophilic aromatic substitution: The four intermediate stages occurring under 2b are referred to as arenium ions.
Arenium ions are characterized by the fact that the aromatic character is temporarily lost through the reaction mechanism and a charged species is created. Arenium ions can be identified as cations, as in the scheme above, or they can appear as anions, such as are often found in nucleophilic aromatic substitution. The existence of these relatively unstable intermediate forms was confirmed experimentally by the isolation of a red potassium salt [2,4,6- (NO 2 ) 3 -1-EtO-1-MeOC 6 H 2 ] - K + (Meisenheimer complex) by X-ray structure analysis and spectroscopy become. Arenium ions are mainly found in aromatic substitution reactions (both in the nucleophilic and electrophilic reaction mode) and in the so-called aryne mechanism . Sometimes arenium cations are also referred to as so-called Wheland complexes or Wheland intermediates (after George Willard Wheland ).
Individual evidence
- ↑ Entry on arenium ions . In: IUPAC Compendium of Chemical Terminology (the “Gold Book”) . doi : 10.1351 / goldbook.A00436 .
literature
- Peter Sykes: How do organic reactions work? 2nd edition, Wiley-VCH 2001 . ISBN 3527303057