After looking at a bunch of IR spectrums for ketones, I have noticed this tiny peak that I circled on the diagram below. Does anyone know what it actually is and if I can always use it to distinguish a ketone vs aldehyde?

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  • 6
    $\begingroup$ It's an overtone peak, double the frequency of the carbonyl. Look at this YouTube. $\endgroup$
    – user55119
    Aug 6 at 0:00
  • 1
    $\begingroup$ Not quite double it is from 1st to 3rd vibrational level. It would be nice to have the frequency. $\endgroup$
    – jimchmst
    Aug 6 at 2:03


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