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C=O stretchings


Carbonyl function

Very intense and a little broad in the presence of hydrogen bonds

Most typical band: νC=O from 1800 to 1600 cm-1

Illustration of a C=O bond. The upper bond is red, with arrows moving away. The lower bond is black, with arrows approaching.

What influences its position

Pictogram attention

Strategy

  • Ketones:
ν C=O ~ 1700 cm-1 + ν C-C-C ~ 1200 cm-1
Illustration ketones : V asym, a C-C bond approaching, a C-C bond moving away, a C=O bond
  • Aldehydes:
ν C=O above 1700 cm-1 + ↘ν C-H ca 2850 and 2700 cm-1 by hydrogen bond + Fermi resonance
  • Esters: 3 intense and rather broad bands
νC=O = 1700 cm-1
νC-C-O = 1200 cm-1
νO-C-C = 1100 cm-1
Illustrations Esters : V asym C-C-O, and V O-C-C
  • Carboxylic acids:
νO-H very broad (several hundreds of cm-1) + νC=O + νC-O and δO-H

  • Carboxylates: 2 intense bands
νasym C=O = 1650-1540 cm-1
νsym C=O = 1450-1360 cm-1
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