I have the following IR Spectrum that I am trying to interpret: enter image description here

So far I am thinking this compound have:

  • a primary amine due to two peaks at 3624 and 3533.
  • The sharp peak 3416 could indicate an alkyne(sp C-H).
  • And the other sharp peak at 1716 is an aldehyde or ketone.

Is this analysis correct ? And what have I missed ? Thanks for any help !


The sharp, intense band at 1716 $\mathrm{cm^{-1}}$ is indeed characteristic for a carbonyl group ($\ce{C=O}$ stretch, in this case aldehyde or ketone). The medium and broad bands between 2732-2957 $\mathrm{cm^{-1}}$ suggest that it is more likely an aldehyde. In this case, they would be assigned to the $\ce{=C-H}$ stretch, and the intensity of the broad band fits better to a saturated aldehyde, i.e. there is no double or triple bond in $\alpha, \beta$-position to the $\ce{CHO}$ group.

Your assignment of the peaks at 3624 and 3533 $\mathrm{cm^{-1}}$ to a primary amine is reasonable, since primary amines have two bands, while a secondary amine would have only one, weaker band at lower wavenumbers. One of the bands in the area of 700-940 $\mathrm{cm^{-1}}$ can then be assigned to the $\ce{N-H}$ wagging vibration mode.

The sharp band at 3416 $\mathrm{cm^{-1}}$ could indicate a terminal alkyne ($\ce{C \equiv C-H}$ stretch), the $\ce{C-H}$ stretch band of this group at approximately 2900 $\mathrm{cm^{-1}}$ would then be included in the broad band at 2957 $\mathrm{cm^{-1}}$. The weak band in the area between 2000-2250 $\mathrm{cm^{-1}}$ can then be assigned to the $\ce{C \equiv C}$ stretch.

Sources: 1, 2, 3, 4

  • $\begingroup$ The band at 3416 might be the aldehyde C-H. goodmolecules.blogspot.com/2013/06/… $\endgroup$ Aug 2 '14 at 15:47
  • $\begingroup$ @brinnb On the linked page, it is stated that the bands at ~2700 and ~2800 belong to the aldehyde CH stretch (which is in range of the bands between 2700-2900 in the spectrum of the OP), and that the band at around 3500 would probably be an overtone of the carbonyl band. Furthermore, this suspected overtone band is significantly less sharp than the 3416 band in the spectrum of the OP. $\endgroup$ Aug 2 '14 at 16:02

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