Hello, can you please tell me the interpretation of this IR spectra of #"1-(2,4-dinitrophenyl)-2"##"-(propan-2-ylidene)"##"hydrazine"#?? Thanks in advance

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May 18, 2017

Based on this spectrum of nitrobenzene from SDBS (http://sdbs.db.aist.go.jp/), I don't think the #"1618 cm"^(-1)# is the imine bond. I think that is one of the #"NO"_2# stretches, since they are very similar shapes.

It may be the weak #bb("1689 cm"^(-1))# peak. I don't know how strong or weak it's supposed to be, but it does reasonably match the first reference spectrum I showed.

(I am referring to the weak shoulder to the left of the two nitro stretches.)

If not, it may be the #bb("1587 cm"^(-1))# peak, since the two nitro groups on the same benzene ring may withdraw electron density away from the imine bond, weakening it.

(A weaker bond has a lower force constant and thus a lower fundamental stretching frequency.)


I searched your compound on http://scifinder.cas.org/, and landed on:

REFERENCE FREQUENCIES

From my text (Techniques in Organic Chemistry 3rd ed. by Mohrig), these are the relevant reference frequencies that I can find off-hand:

  • #bb("NO"_2)# stretches (#"1570 - 1490 cm"^(-1), "1390 - 1300 cm"^(-1)#, strong)
  • Aromatic
    #"C"="C"# stretch (#"1620 - 1440 cm"^(-1)#, medium to weak),
    #"C"-"H"# stretch (#"3100 - 3000 cm"^(-1)#, medium to weak),
    #"C"-"H"# bend (#"900 - 680 cm"^(-1)"#, strong)
  • Amines
    #"N"-"H"# stretch (#"3550 - 3250 cm"^(-1)#, medium;
    #2^@# amine #=># one band)
  • Alkanes
    #"C"-"H"# stretch (#"2990 - 2850 cm"^(-1)#, medium to strong)

Overall, here's what I came up with:

REFERENCE SPECTRA

To compare, here is a spectrum from the Bio-Rad/Sadtler IR Data Collection (Bio-Rad Laboratories, Philadelphia, PA), taken with a BIO-RAD DIGILAB FT-IR:

Since the amine frequencies weren't clear, another reference spectrum is from the Integrated Spectral Database System of Organic Compounds (National Institute of Advanced Industrial Science and Technology [Japan]), taken with a JASCO FT/IR-410:

Lastly, this website reports about #"1660 cm"^(-1)# for the #"C"="N"# stretch.

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