Dear Indria,

It is a well know fact that the carbonyl absortion is strongly influenced by conjugation, in your case with multiple double bonds.

You can compare your spectrum with the IR spectra of enones, a carbonyl vibration at about 1650 and a C=C at 1600 cm-1.

In your spectrum the C=O lies at 1650 cm-1 and the numerous C=C signals are mixing with the ortho-aromatic signals and in this way create a stronger band at 1574 and 1600 cm-1.

in my opinion where the peak is in terms of wavenumbers is more important than intensity. I looked at a lot of literature spectra of diazonium salts and some of the N2 stretch were very very strong and others were medium. However they were all near the same wavenumbers.

1574 cm-1 is too far for ketone. You could also do 13C NMR to confirm ketone. Ketones give chemical shift around 200 ppm I believe, farther than any other carbonyl.

Dear Indria,

It is a well know fact that the carbonyl absortion is strongly influenced by conjugation, in your case with multiple double bonds.

You can compare your spectrum with the IR spectra of enones, a carbonyl vibration at about 1650 and a C=C at 1600 cm-1.

In your spectrum the C=O lies at 1650 cm-1 and the numerous C=C signals are mixing with the ortho-aromatic signals and in this way create a stronger band at 1574 and 1600 cm-1.

1650 is your carbonyl peak. It can be confirmed by 13C NMR as Greg suggested.

Engines, conjugated ketones are expected to give absorption in the range of 1650 - 1700cm-1, the intensity depends on esoteric factors, conjugation and the presence of conjugated aromatic system. In this case C=C absorbs in the range of 1550-1600 cm-1. In the resonance structures C=O and C-O (ionic) the latter is more contributing while for C=C and C-C equally contributing causing the increase in intensity.

The C13 NMR shows signal in the range of 180 - 200 ppm confirming the presence of C=O group.