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IR8. More Complicated IR Spectra

  • Page ID
    4175
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    Sometimes more complicated heteroatomic functional groups, containing bonds to more than one heteroatom, have slightly different spectra. Carboxylic acids feature a hydroxyl group bonded to a carbonyl. Hexanoic acid, a carboxylic acid in a six-atom chain, is one example.

    hexanoic acid.gif

    If you look at the IR spectrum of hexanoic acid:

    • IRFig12.gif

      Source: SDBSWeb : http://riodb01.ibase.aist.go.jp/sdbs/ (National Institute of Advanced Industrial Science and Technology of Japan, 14 July 2008)

      At first, the O-H peak appears to be absent. The C-H stretch appears to be very broad. The wide peak between 3000 and 2600 cm-1 is really the usual C-H stretch with a broad O-H stretch superimposed on it. The low frequency vibration of this O-H bond is related to the partial dissociation of protons due to strong hydrogen bonding.


    IR8. More Complicated IR Spectra is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by Chris Schaller.

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