https://doi.org/10.1351/goldbook.A00129
Acyl intermediates include acyl anions, acyl radicals and acyl cations (synonym acylium ions) which are formally derived from oxoacids RkE(=O)l(OH)m (l ≠ 0) by removal of a hydroxyl cation HO+, a hydroxyl radical HO. or a hydroxyl anion HO−, respectively, and replacement analogues of such intermediates. Acyl anions, radicals and cations can formally be represented by canonical forms having a negative charge, an unpaired electron or a positive charge on the acid-generating element of the oxoacid. Acyl anions. E.g.
Acyl radicals. E.g.
Acyl cations. E.g. 
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See also: acyl groups
Sources:
PAC, 1993, 65, 1357. (Revised nomenclature for radicals, ions, radical ions and related species (IUPAC Recommendations 1993)) on page 1357 [Terms] [Paper]
PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1312 [Terms] [Paper]
PAC, 1993, 65, 1357. (Revised nomenclature for radicals, ions, radical ions and related species (IUPAC Recommendations 1993)) on page 1357 [Terms] [Paper]
PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1312 [Terms] [Paper]