COSchwingung

COSchwingung, in German often written as CO-Schwingung, refers to the vibrational mode in which the carbon–oxygen bond changes length during vibration. It is a fundamental type of molecular vibration observed in infrared spectroscopy and can describe both the diatomic CO molecule and carbonyl-containing functional groups (C=O) in larger molecules. In IR spectra, the COSchwingung typically appears as a strong absorption band, whose position and intensity depend on the chemical environment of the bond.

For the diatomic carbon monoxide, the fundamental COSchwingung occurs at about 2140 cm^-1 in the gas phase, reflecting the high bond strength of the C≡O bond. In carbonyl-containing compounds, the C=O stretching vibration gives rise to bands in a broader range, typically from roughly 1650 to 1850 cm^-1. The exact position depends on factors such as conjugation, resonance, ring strain, and substituents: conjugation and resonance with adjacent π systems or heteroatoms generally lower the frequency, while reduced delocalization or stronger bond character tends to raise it. Hydrogen bonding to the carbonyl oxygen also shifts the band to lower wavenumbers. Isotopic substitution (for example 13C or 18O) shifts the COSchwingung to lower frequencies, reflecting the change in reduced mass.

Applications of COSchwingung analysis include identifying functional groups, assessing carbonyl content, and studying reaction mechanisms or environment effects in organic chemistry, biochemistry, and materials science. Limitations arise from overlapping bands and variations due to solvent, temperature, and matrix effects. See also infrared spectroscopy, carbonyl group, and vibrational spectroscopy.