Formyl cation, [HCO]+. Abundant in space, intermediate in the Gattermann-Koch reaction[1]. Can generate from formyl fluoride and antimony pentafluoride:[2]

HC(O)F + SbF5 → [HCO]+ + [SbF6]

Can consider as protonated carbon monoxide (H+ + CO → HCO+), or formaldehyde from which a hydride ion has been abstracted (H2CO → H + HCO+).

Structure

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X 1Σ+ state, MW, 2008[3]
configuration interaction, 1976[4]
Spartan HF 6-31G*
Sortable table
Species Formula CO bond order r(C-O) / Å r(C-H) / Å technique ref
carbon monoxide CO 3 1.128 - ? G&E
formyl cation HCO+ 3 1.1107 1.0933 MW [3]
formyl radical HCO 2 1.1712 1.1110 MW [5]
formaldehyde H2CO 2 1.209 1.116 MW [5]
methanol H3COH 1 1.4246 1.0936 MW [5]

Problem: bond lengths indicate C-O triple bond, but Lewis structure with C-O triple bond has wrong charges: +ve O and H, neutral C, whereas HF indicates neutral O, +ve C and H. Not just a simple matter of superimposing Lewis structures' wavefunctions - or is it?

Refs

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  1. ^ J. Org. Chem. (1995) 60, 3846–3850
  2. ^ J. Phys. Chem. B (2001) 105, 8212–8219
  3. ^ a b J. Chem. Phys. (2008) 129, 164311
  4. ^ Astrophys. J. (1976) 205, L97-L100
  5. ^ a b c Lide, David R. (2008). CRC Handbook of Chemistry and Physics, 89th Edition. CRC Press. p. 9-36. ISBN 978-0849304880.