In FTIR, for example, the carbonyl group peak of an amide ligand shifts negatively at lower frequencies when it participates in a coordination. However, it is observed in Raman that the frequency increased in the same compound. Is this possible ?, does it have logic? Does this happen in the Raman?
the vibrational modes of functional groups vary if their electron inventory is changed.
In your case it looks that upon coordination to a metal (electrophile) the electron density of the C=O group is reduced partly removing electrons from the double bond and thus the C=O stretching frequency is decreased.
This is expectable (logic) and you will see it in Raman and IR spectra.
Raman or IR have different selection rules but they show the same vibrations, tortions and waggings at the same energies.
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