https://doi.org/10.1351/goldbook.A00436
Cations derived formally by the addition of a @H02904@ or other cationic species to any position of an arene, e.g. C6H7+, benzenium. The term includes:
  1. Arenium σ-adducts (Wheland intermediates) (which are considered to be intermediates in electrophilic aromatic substitution reactions) and other @C01502@.
    A00436-1.png
  2. Arenium π-adducts, such as:
    A00436-2.png
[σ-@A00138@ (sigma-@A00138@), π-@A00138@ (pi-@A00138@)].
Source:
PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1318 [Terms] [Paper]
See also:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1077 [Terms] [Paper]